Simulation And Design Of Soft Robotic Swimmers With Artificial Muscle Andrew Michael Hess

Simulation And Design Of Soft Robotic Swimmers
With Artificial Muscle Andrew Michael Hess
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SIMULATION AND DESIGN OF SOFT ROBOTIC SWIMMERS WITH ARTIFICIAL
MUSCLE
By
Andrew Michael Hess
A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
Mechanical Engineering – Doctor of Philosophy
Computational Mathematics, Science, and Engineering – Dual Major
2019

ProQuest Number:
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INFORMATION TO ALL USERS
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In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted. Also, if material had to be removed,
a note will indicate the deletion.
Published by ProQuest LLC (
ProQuest
). Copyright of the Dissertation is held by the Author.
All Rights Reserved.
This work is protected against unauthorized copying under Title 17, United States Code
Microform Edition © ProQuest LLC.
ProQuest LLC
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27666439
27666439
2019

ABSTRACT
SIMULATION AND DESIGN OF SOFT ROBOTIC SWIMMERS WITH ARTIFICIAL
MUSCLE
By
Andrew Michael Hess
Soft robots take advantage of rich nonlinear dynamics and large degrees of freedom to perform
actions often by novel means beyond the capability of conventional rigid robots. Nevertheless, there
are considerable challenges in analysis, design, and optimization of soft robots due to their complex
behaviors. This is especially true for soft robotic swimmers whose dynamics are determined by
highly nonlinear fluid-structure interactions. We present a holistic computational framework that
employs a multi-objective evolutionary method to optimize feedback controllers for maneuvers of
a soft robotic fish under artificial muscle actuation.
The resultant fluid-structure interactions are fully solved by using a novel fictitious domain/active
strain method, developed to numerically study the swimming motion of thin, light-weight soft
robots composed of smart materials that can actively undergo reversible large deformations. We
assume the elastic material to be neo-Hookean, and behave like an artificial “muscle” which, when
stimulated, generates a principal stretch of contraction. Instead of imposing active stresses, here we
adopt an active strain approach to impose contracting strains to drive elastic deformation following
a multiplicative decomposition of the deformation gradient tensor. The hydrodynamic coupling
between the fluid and the solid is then resolved by using the fictitious domain method where the
induced flow field is virtually extended into the solid domain. Pseudo body forces are employed
to enforce the interior fictitious fluid motion to be the same as the structural movement. To
demonstrate this method we carry out a series of numerical explorations for soft robotic swimmers
of both 2D and 3D geometries that prove these robot prototypes can effectively perform undulatory
and jet-propulsion locomotion when active contracting strains are appropriately distributed on
elastica.

To complete our framework we then demonstrate the design and optimization of a maneuverable,
undulatory, soft robotic fish. In particular, we consider a two-dimensional elastic plate with
finite thickness, subjected to active contractile strains on both sides of the body. Compared
to the conventional approaches that require specifying the entire-body curvature variation, we
demonstrate that imposing contractile active strains locally can produce various swimming gaits,
such as forward swimming and turning, using far fewer control parameters. The parameters of
a pair of proportional-integral-derivative (PID) controllers, used to control the amplitude and the
bias of the active strains, respectively, are optimized for tracking a moving target involving different
trajectories and Reynolds numbers, with three objectives, tracking error, cost of transport, and
elastic strain energy. The resulting Pareto fronts of the multi-objective optimization problem reveal
the correlation and trade-off among the objectives and offer key insight into the design and control
of soft swimmers.
Furthermore, we expand upon these core studies by investigating a variety processes and
phenomena that are of potential importance to the design of soft robotic fish. Rich and complex
phenomena occur at the interface between fluids and elastic solids that can influence the behavior
of the overall system. This is especially true in the case of soft robots where wrinkling, folding,
and similar wavelike behavior can occur at the surface and affect the momentum transfer which is
necessary to produce locomotion. To begin to understand this behavior we analytically investigate
the linear stability of a viscoelastic gel-like film subjected to Newtonian Couette flow in the limit
of vanishing Reynolds number.
The final avenue of study attempts to answer the question of how to design and optimize the
body shape in conjunction with the actuation scheme of a soft robotic fish. The flexibility of soft
materials and actuators lead to large degrees of freedom creating a wide array of possibilities but
at the same time overwhelming the traditional design process. We demonstrate a viable solution
to this issue by using evolutionary optimization to simultaneously optimize both the shape and
actuation of a simple 2D soft robotic fish in a simple case study.

Copyright by
ANDREW MICHAEL HESS
2019

Dedicated to my parents, whose support and patience made all of this possible.
v

ACKNOWLEDGEMENTS
First and foremost I would like to thank my advisor, Dr. Tong Gao, for his expertise and guidance
throughout the projects that make up this dissertation. As his first doctoral student, this process
was a learning experience for us both and I believe one that left us both the better for it. I hope that
the feeling is mutual and that our continued collaborations will bear fruit for years to come.
I would like to thank my committee members, Dr. Farhad Jaberi, Dr. Ahmed Naguib, and Dr.
Mohsen Zayernouri for their support, suggestions, and imparted wisdom from the beginning as I
sat in their classrooms to the very end as I stood before them to defend my work.
I gratefully acknowledge my collaborators such as Dr. Xiaobo Tan and Dr. Zhaowu Lin among
innumerable others who have and continue to share their knowledge and expertise without which
none of this would have been possible.
Last but not least, I thank those who supported me through thick and thin. Mom & Dad and
my grandparents who were always there for me regardless of how rocky the path, at times, became.
Brittany, my longtime partner in crime, who stuck with me from undergrad through all the trials
and tribulations that lead to us each becoming some variety of “Dr”. And friends new and old
whose companionship kept me sane along the way, Krissy, Coco, Mattei, Seward, Kevin, Chris,
Rachel, Joe, Chad, Taylor, Connor, Sanders, ...
vi

TABLE OF CONTENTS
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
CHAPTER 1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
CHAPTER 2 STABILITY OF COUETTE FLOW PAST A GEL FILM . . . . . . . . . . . 4
2.1 Mathematical Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Constitutive equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Universal Eulerian description . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Linear Stability Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.1 Base state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2 Normal modes and interfacial conditions . . . . . . . . . . . . . . . . . . . 10
2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.1 Growth Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.2 Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.3 Marginal Instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
CHAPTER 3 A FLUID–STRUCTURE INTERACTION STUDY OF SOFT ROBOTIC
SWIMMER USING A FICTITIOUS DOMAIN/ACTIVE-STRAIN METHOD 19
3.1 Mathematical Model and Numerical Method . . . . . . . . . . . . . . . . . . . . . 20
3.1.1 Hill’s Muscle Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.2 Active Strain Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.3 Distributed Lagrange Multiplier/Fictitious Domain Method (DLM/FD) . . . 23
3.1.3.1 Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.3.2 Numerical scheme . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1.3.3 Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2.1 Two-Dimensional Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2.2 Three-Dimensional Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2.2.1 Deformation Control . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2.2.2 Undulatory Swimming . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.2.3 Jet-propulsion Swimming . . . . . . . . . . . . . . . . . . . . . 40
CHAPTER 4 CFD-BASED MULTI-OBJECTIVE CONTROLLER OPTIMIZATION
FOR SOFT ROBOTIC FISH WITH MUSCLE-LIKE ACTUATION . . . . . 47
4.1 Mathematical Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2 Controller Design and Optimization . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.2.1 Control Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.2.2 Multi-Objective Optimization . . . . . . . . . . . . . . . . . . . . . . . . 54
vii

4.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3.1 Undulatory Swimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3.2 Optimization and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.3.2.1 Trajectory Comparison . . . . . . . . . . . . . . . . . . . . . . . 58
4.3.2.2 Pareto Fronts of Optimized Solutions . . . . . . . . . . . . . . . 60
4.3.2.3 Objective Correlations and Parameter Trends . . . . . . . . . . . 62
CHAPTER 5 FUTURE WORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.1 Body Shape Optimization for Muscle Driven Undulatory Swimming . . . . . . . . 67
CHAPTER 6 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
viii

LIST OF TABLES
Table 3.1: The amplitude of the central point on the free end and the Strouhal number
and the average drag coefficient for a flexible beam . . . . . . . . . . . . . . . . 29
Table 3.2: The amplitude of the central point on the plate trailing edge and the Strouhal
number and the average drag coefficient for a flag flapping in uniform flow. . . . 30
Table 4.1: Summary of the variables (PID tuning parameters) and objectives considered
in the optimization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
ix

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SIN ON THE CONSCIENCE
It is of the utmost importance that we accurately distinguish
between sin in the flesh, and sin on the conscience. If we confound
these two, our souls must necessarily be unhinged, and our worship
marred. An attentive consideration of 1 John i. 8-10. will throw much
light upon this subject, the understanding of which is so essential.
There is no one who will be so conscious of indwelling sin, as the
man who walks in the light. "If we say that we have no sin, we
deceive ourselves, and the truth is not in us." In the verse
immediately preceding, we read, "the blood of Jesus Christ His Son
cleanseth us from all sin." Here the distinction between sin in us,
and sin on us, is fully brought out and established. To say that there
is sin on the believer, in the presence of God, is to call in question
the purging efficacy of the blood of Jesus, and to deny the truth of
the divine record. If the blood of Jesus can perfectly purge, then the
believer's conscience is perfectly purged. The word of God thus puts
the matter; and we must ever remember that it is from God Himself
we are to learn what the true condition of the believer is, in His
sight. We are more disposed to be occupied in telling God what we
are in ourselves, than to allow Him to tell us what we are in Christ.
In other words, we are more taken up with our own self-
consciousness, than with God's revelation of Himself. God speaks to
us on the ground of what He is in Himself, and of what He has
accomplished in Christ. Such is the nature and character of His
revelation, of which faith takes hold, and thus fills the soul with
perfect peace. God's revelation is one thing; my consciousness is
quite another.
But the same word which tells us we have no sin on us, tells us, with
equal force and clearness, that we have sin in us. "If we say we
have no sin, we deceive ourselves, and the truth is not in us." Every

one who has "truth" in him, will know that he has "sin" in him,
likewise; for truth reveals everything as it is. What, then, are we to
do? It is our privilege so to walk in the power of the new nature
(that is, the Holy Ghost), that the "sin" which dwells in us may not
manifest itself in the form of "sins." The Christian's position is one of
victory and liberty. He is not only delivered from the guilt of sin, but
also from sin as a ruling principle in his life. "Knowing this, that our
old man is crucified with him, that the body of sin might be
destroyed, that henceforth we should not serve sin. For he that is
dead is freed from sin ... let not sin therefore reign in your mortal
body, that ye should obey it in the lusts thereof.... For sin shall not
have dominion over you; for ye are not under the law, but under
grace." (Rom. vi. 6-14.) Sin is there in all its native vileness, but the
believer is dead to it. How? He died in Christ. By nature he was dead
in sin. By grace he is dead to it. What claim can anything or any one
have upon a dead man? None whatever. Christ "died unto sin once,"
and the believer died in Him. "Now if we be dead with Christ, we
believe that we shall also live with Him; knowing that Christ, being
raised from the dead, dieth no more; death hath no more dominion
over Him. For in that He died, He died unto sin once; but in that He
liveth, He liveth unto God." What is the result of this, in reference to
believers? "Likewise reckon ye also yourselves to be dead indeed
unto sin, but alive unto God through Jesus Christ our Lord." Such is
the believer's unalterable position before God, so that it is his holy
privilege to enjoy freedom from sin as a ruler over him, though it be
a dweller in him.
But then, "if any man sin," what is to be done? The inspired apostle
furnishes a full and most blessed answer: "If we confess our sins, He
is faithful and just to forgive us our sins, and to cleanse us from all
unrighteousness." (1 John i. 9.) Confession is the mode in which the
conscience is to be kept free. The apostle does not say, "If we pray
for pardon, He is gracious and merciful to forgive us." No doubt, it is
ever happy for a child to breathe the sense of need into his father's
ear—to tell him of feebleness, to confess folly, infirmity, and failure.
All this is most true; and, moreover, it is equally true that our Father

is most gracious and merciful to meet His children in all their
weakness and ignorance; but, while all this is true, the Holy Ghost
declares, by the apostle, that "if we confess," God is "faithful and
just to forgive." Confession therefore is the divine mode. A Christian,
having erred in thought, word, or deed, might pray for pardon for
days and months together, and not have any assurance, from 1 John
i. 9, that he was forgiven; whereas, the moment he truly confesses
his sin before God, it is a simple matter of faith to know that he is
perfectly forgiven, and perfectly cleansed.
There is an immense moral difference between praying for
forgiveness, and confessing our sins, whether we look at it in
reference to the character of God, the sacrifice of Christ, or the
condition of the soul. It is quite possible that a person's prayer may
involve the confession of his sin, whatever it may happen to be, and
thus come to the same thing. But then, it is always well to keep
close to Scripture, in what we think, and say, and do. It must be
evident that when the Holy Ghost speaks of confession, He does not
mean praying. And it is equally evident that He knows there are
moral elements in, and practical results flowing out of, confession,
which do not belong to prayer. In point of fact, one has often found
that a habit of importuning God for the forgiveness of sins, displayed
ignorance as to the way in which God has revealed Himself in the
Person and work of Christ; as to the relation in which the sacrifice of
Christ has set the believer; and as to the divine mode of getting the
conscience relieved from the burden, and purified from the evil of
sin.
God has been perfectly satisfied, as to all the believer's sins, in the
cross of Christ. On that cross a full atonement was presented for
every jot and tittle of sin, in the believer's nature and on his
conscience. Hence, therefore, God does not need any further
propitiation. He does not need aught to draw His heart toward the
believer. We do not require to supplicate Him to be "faithful and
just," when His faithfulness and justice have been so gloriously
displayed, vindicated, and answered, in the death of Christ. Our sins

can never come into God's presence, inasmuch as Christ, who bore
them all, and put them away, is there instead. But if we sin,
conscience will feel it, must feel it; yea, the Holy Ghost will make us
feel it. He cannot allow so much as a single light thought to pass
unjudged. What then? Has our sin made its way into the presence of
God? Has it found its place in the unsullied light of the inner
sanctuary? God forbid! The "Advocate" is there—"Jesus Christ the
righteous"—to maintain, in unbroken integrity, the relationship in
which we stand. But though sin cannot affect God's thoughts in
reference to us, it can, and does affect our thoughts in reference to
Him. Though it cannot make its way into God's presence, it can
make its way into ours, in a most distressing and humiliating
manner. Though it cannot hide the Advocate from God's view, it can
hide Him from ours. It gathers, like a thick dark cloud, on our
spiritual horizon, so that our souls cannot bask in the blessed beams
of our Father's countenance. It cannot affect our relationship with
God, but it can very seriously affect our enjoyment thereof. What,
therefore, are we to do? The Word answers, "If we confess our sins,
He is faithful and just to forgive us our sins, and to cleanse us from
all unrighteousness." By confession, we get our conscience cleared;
the sweet sense of our relationship restored; the dark cloud
dispersed; the chilling, withering influence removed; our thoughts of
God set straight. Such is the divine method; and we may truly say
that the heart that knows what it is to have ever been in the place of
confession, will feel the divine power of the apostle's words, "My
little children, these things write I unto you, that ye sin not." (1 John
ii. 1.)
Then, again, there is a style of praying for forgiveness which
involves a losing sight of the perfect ground of forgiveness, which
has been laid in the sacrifice of the cross. If God forgives sins, He
must be "faithful and just" in so doing. But it is quite clear that our
prayers, be they ever so sincere and earnest, could not form the
basis of God's faithfulness and justice in forgiving us our sins.
Nought save the work of the cross could do this. There the
faithfulness and justice of God have had their fullest establishment,

and that, too, in immediate reference to our actual sins, as well as to
the root thereof, in our nature. God has already judged our sins, in
the Person of our Substitute, "on the tree;" and, in the act of
confession, we judge ourselves. This is essential to divine
forgiveness and restoration. The very smallest unconfessed,
unjudged sin, on the conscience, will entirely mar our communion
with God. Sin in us need not do this; but if we suffer sin to remain
on us, we cannot have fellowship with God. He has put away our
sins in such a manner as that He can have us in His presence; and
so long as we abide in His presence, sin does not trouble us. But if
we get out of His presence, and commit sin, our communion must of
necessity be suspended until, by confession, we have got rid of the
sin. All this, I need hardly add, is founded exclusively upon the
perfect sacrifice and righteous advocacy of the Lord Jesus Christ.
Finally, as to the difference between prayer and confession, as
respects the condition of the heart before God, and its moral sense
of the hatefulness of sin, it cannot possibly be overestimated. It is a
much easier thing to ask in a general way for the forgiveness of our
sins, than to confess those sins. Confession involves self-judgment;
asking for forgiveness may not, and in itself does not. This alone
would be sufficient to point out the difference. Self-judgment is one
of the most valuable and healthful exercises of the Christian life; and
therefore anything which produces it must be highly esteemed by
every earnest Christian.
The difference between asking for pardon, and confessing the sin, is
continually exemplified in dealing with children. If a child has done
anything wrong, he finds much less difficulty in asking his father to
forgive him, than in openly and unreservedly confessing the wrong.
In asking for forgiveness, the child may have in his mind a number
of things which tend to lessen the sense of the evil; he may be
secretly thinking that he was not so much to blame after all, though,
to be sure, it is only proper to ask his father to forgive him; whereas,
in confessing the wrong, there is just one thing, and that is self-
judgment. Further, in asking for forgiveness, the child may be

influenced mainly by a desire to escape the consequences of his
wrong; whereas a judicious parent will seek to produce a just sense
of its moral evil, which can only exist where there is the full
confession of the fault in connection with self-judgment.
Thus it is in reference to God's dealing with His children, when they
do wrong. He must have the whole thing brought out and
thoroughly judged. He will make us not only dread the
consequences of sin,—which are unutterable,—but hate the thing
itself, because of its hatefulness in His sight. Were it possible for us,
when we commit sin, to be forgiven merely for the asking, our sense
of sin, and our shrinking from it, would not be nearly so intense;
and, as a consequence, our estimate of the fellowship with which we
are blessed would not be nearly so high. The moral effect of all this
upon the general tone of our spiritual constitution, and also upon
our whole character and practical career, must be obvious to every
experienced Christian.

GOD'S WAY, AND HOW TO FIND IT
(Read Job xxviii.; Luke xi. 34-36.)
"There is a path which no fowl knoweth, and which the vulture's eye
hath not seen: the lion's whelps have not trodden it, nor the fierce
lion passed by it." What an unspeakable mercy for one who really
desires to walk with God, to know that there is a way for him to walk
in! God has prepared a pathway for His redeemed in which they may
walk with all possible certainty, calmness and fixedness. It is the
privilege of every child of God, and every servant of Christ, to be as
sure that he is in God's way as that his soul is saved. This may seem
a strong statement; but the question is, Is it true? If it be true, it
cannot be too strong. No doubt it may, in the judgment of some,
savor a little of self-confidence and dogmatism to assert, in such a
day as that in which we live, and in the midst of such a scene as
that through which we are passing, that we are sure of being in
God's path. But what saith the Scripture? It declares "there is a
way," and it also tells us how to find and how to walk in that way.
Yes; the self-same voice that tells us of God's salvation for our souls,
tells us also of God's pathway for our feet;—the very same authority
that assures us that "he that believeth on the Son of God hath
everlasting life," assures us also that there is a way so plain that
"the wayfaring men though fools shall not err therein."
This, we repeat, is a signal mercy—a mercy at all times, but
especially in a day of confusion and perplexity like the present. It is
deeply affecting to notice the state of uncertainty in which many of
God's dear people are found at the present moment. We do not refer
now to the question of salvation, of this we have spoken largely
elsewhere; but that which we have now before us is the path of the
Christian—what he ought to do, where he should be found, how he

ought to carry himself in the midst of the professing Church. Is it not
too true that multitudes of the Lord's people are at sea as to these
things? Are there not many who, were they to tell out the real
feelings of their hearts, would have to own themselves in a
thoroughly unsettled state—to confess that they know not what to
do, or where to go, or what to believe? Now, the question is, Would
God leave His children, would Christ leave His servants, in such
darkness and confusion?
"No; my dear Lord, in following Thee,
And not in dark uncertainty,
This foot obedient moves."
May not a child know the will of his father? May not a servant know
the will of his master? And if this be so in our earthly relationships,
how much more fully may we count upon it in reference to our
Father and Master in heaven. When Israel of old emerged from the
Red Sea, and stood upon the margin of that great and terrible
wilderness which lay between them and the land of promise, how
were they to know their way? The trackless sand of the desert lay all
around them. It was in vain to look for any footprint there. It was a
dreary waste in which the vulture's eye could not discern a pathway.
Moses felt this when he said to Hobab, "Leave us not, I pray thee;
forasmuch as thou knowest how we are to encamp in the
wilderness, and thou mayest be to us instead of eyes." (Numb. x.
31.) How well our poor unbelieving hearts can understand this
touching appeal! How one craves a human guide in the midst of a
scene of perplexity! How fondly the heart clings to one whom we
deem competent to give us guidance in moments of darkness and
difficulty!
And yet, we may ask, what did Moses want with Hobab's eyes? Had
not Jehovah graciously undertaken to be their guide? Yes, truly; for
we are told that "on the day that the tabernacle was reared up, the
cloud covered the tabernacle, namely, the tent of the testimony; and
at even, there was upon the tabernacle as it were the appearance of

fire, until the morning. So it was alway: the cloud covered it by day,
and the appearance of fire by night. And when the cloud was taken
up from the tabernacle, then after that the children of Israel
journeyed; and in the place where the cloud abode, there the
children of Israel pitched their tents. At the commandment of the
Lord the children of Israel journeyed, and at the commandment of
the Lord they pitched: as long as the cloud abode upon the
tabernacle, they rested in their tents. And when the cloud tarried
long upon the tabernacle many days, then the children of Israel kept
the charge of the Lord, and journeyed not. And so it was, when the
cloud was a few days upon the tabernacle; according to the
commandment of the Lord they abode in their tents, and according
to the commandment the Lord, and journeyed not. And so it was,
when the cloud abode from even unto the morning, and that the
cloud was taken up in the morning, then they journeyed; whether it
was by day or by night that the cloud was taken up, they journeyed;
or whether it were two days, or a month, or a year, that the cloud
tarried upon the tabernacle, remaining thereon, the children of Israel
abode in their tents and journeyed not, but when it was taken up
they journeyed. At the commandment of the Lord they rested in
their tents, and at the commandment of the Lord they journeyed:
they kept the charge of the Lord at the commandment of the Lord
by the hand of Moses" (Num. ix. 15-23).
Here was divine guidance—a guidance, we may surely say, quite
sufficient to render them independent of their own eyes, of Hobab's
eyes, and the eyes of any other mortal. It is interesting to note that
in the opening of the book of Numbers, it was arranged that the ark
of the covenant was to find its place in the very bosom of the
congregation; but in chapter x. we are told that when "they
departed from the mount of the Lord three days' journey, the ark of
the covenant of the Lord went before them, in the three days'
journey, to search out a resting-place for them." Instead of Jehovah
finding a resting-place in the bosom of His redeemed people, He
becomes their traveling Guide, and goes before them to seek out a
resting-place for them. What touching grace is here! and what

faithfulness! If Moses will ask Hobab to be their guide, and that, too,
in the very face of God's provision—even the cloud and the silver
trumpet, then will Jehovah leave His place in the centre of the tribes,
and go before them to search them out a resting-place. And did not
He know the wilderness well? Would not He be better for them than
ten thousand Hobabs? Might they not fully trust Him? Assuredly. He
would not lead them astray. If His grace had redeemed them from
Egypt's bondage, and conducted them through the Red Sea, surely
they might confide in the same grace to guide them across that
great and terrible wilderness, and bring them safely into the land
flowing with milk and honey.
But it must be borne in mind that, in order to profit by divine
guidance, there must be the abandonment of our own will, and of all
confidence in our own reasonings, as well as all confidence in the
thoughts and reasonings of others. If I have Jehovah as my Guide, I
do not want my own eyes or the eyes of a Hobab either. God is
sufficient: I can trust Him. He knows all the way across the desert;
and hence, if I keep my eye upon Him, I shall be guided aright.
But this leads us on to the second division of our subject, namely,
How am I to find God's way? An all-important question, surely.
Whither am I to turn to find God's pathway? If the vulture's eye, so
keen, so powerful, so far-seeing, hath not seen it,—if the young lion,
so vigorous in movement, so majestic in mien, hath not trodden it,—
if man knoweth not the price of it, and if it is not to be found in the
land of the living,—if the depth saith, It is not in me, and the sea
saith, It is not with me,—if it cannot be gotten for gold or precious
stones,—if the wealth of the universe cannot equal it, and no wit of
man discover it,—then whither am I to turn? where shall I find it?
Shall I turn to those great standards of orthodoxy which rule the
religious thought and feeling of millions throughout the length and
breadth of the professing Church? Is this wondrous pathway of
wisdom to be found with them? Do they form any exception to the
great, broad, sweeping rule of Job xxviii? Assuredly not. What, then,
am I to do? I know there is a way. God, who cannot lie, declares

this, and I believe it; but where am I to find it? "Whence, then,
cometh wisdom? and where is the place of understanding? seeing it
is hid from the eyes of all living, and kept close from the fowls of the
air. Destruction and Death say, We have heard the fame thereof with
our ears." Does it not seem like a hopeless case for any poor
ignorant mortal to search for this wondrous pathway? No, blessed be
God, it is by no means a hopeless case, for "He understandeth the
way thereof, and He knoweth the place thereof. For He looketh to
the ends of the earth, and seeth under the whole heaven; to make
the weight for the winds; and He weigheth the waters by measure.
When He made a decree for the rain, and a way for the lightning of
the thunder, then did He see it and declare it; He prepared it, yea,
and searched it out. And unto man He said, 'Behold, the fear of the
Lord, that is wisdom; and to depart from evil is understanding.'"
Here, then, is the divine secret of wisdom: "The fear of the Lord."
This sets the conscience directly in the presence of God, which is its
only true place. The object of Satan is to keep the conscience out of
this place—to bring it under the power and authority of man—to
lead it into subjection to the commandments and doctrines of men—
to thrust in something between the conscience and the authority of
Christ the Lord, it matters not what it is; it may be a creed or a
confession containing a quantity of truth,—it may be the opinion of a
man or a set of men—the judgment of some favorite teacher,—
anything, in short, to come in and usurp, in the heart, the place
which belongs to God's Word alone. This is a terrible snare, and a
stumbling-block—a most serious hindrance to our progress in the
ways of the Lord. God's Word must rule me—God's pure and simple
Word, not man's interpretation thereof. No doubt, God may use a
man to unfold that Word to my soul; but then it is not man's
unfolding of God's Word that rules me, but God's Word by man
unfolded. This is of all importance. We must be exclusively taught
and exclusively governed by the Word of the living God. Nothing else
will keep us straight, or give solidity and consistency to our character
and course as Christians. There is a strong tendency within and
around us to be ruled by the thoughts and opinions of men—by

those great standards of doctrine which men have set up. Those
standards and opinions may have a large amount of truth in them—
they may be all true so far as they go; that is not the point in
question now. What we want to impress upon the Christian reader
is, that he is not to be governed by the thoughts of his fellow-man,
but simply and solely by the Word of God. It is of no value to hold a
truth from man; I must hold it directly from God Himself. God may
use a man to communicate His truth; but unless I hold it as from
God, it has no divine power over my heart and conscience; it does
not bring me into living contact with God, but actually hinders that
contact by bringing in something between my soul and His holy
authority.
We should greatly like to enlarge upon and enforce this great
principle; but we must forbear, just now, in order to unfold to the
reader one or two solemn and practical points set forth in the
eleventh chapter of Luke,—points which, if entered into, will enable
us to understand a little better how to find God's way. We shall
quote the passage at length.—"The light of the body is the eye:
therefore when thine eye is single, thy whole body also is full of
light; but when thine eye is evil, thy body also is full of darkness.
Take heed, therefore, that the light which is in thee be not darkness.
If thy whole body therefore be full of light, having no part dark, the
whole shall be full of light, as when the bright shining of a candle
doth give thee light."
Here, then, we are furnished with the true secret of discerning God's
way. It may seem very difficult, in the midst of the troubled sea of
christendom, to steer one's course aright. So many conflicting voices
fall on the ear. So many opposing views solicit our attention, men of
God differ so in judgment, shades of opinion are so multiplied, that it
seems impossible to reach a sound conclusion. We go to one man
who, so far as we can judge, seems to have a single eye, and he
tells us one thing; we go to another man who also seems to have a
single eye, and he tells the very reverse. What, then, are we to
think? Well, one thing is certain, that our own eye is not single when

we are running, in uncertainty and perplexity, from one man to
another. The single eye is fixed on Christ alone, and thus the body is
filled with light. The Israelite of old had not to run hither and thither
to consult with his fellow as to the right way. Each had the same
divine guide, namely, the pillar of cloud by day, and the pillar of fire
by night. In a word, Jehovah Himself was the infallible Guide of each
member of the congregation. They were not left to the guidance of
the most intelligent, sagacious, or experienced man in the assembly;
neither were they left to follow their own way,—each was to follow
the Lord. The silver trumpet announced to all alike the mind of God;
and no one whose ear was open and attentive was left at any loss.
The eye and the ear of each were to be directed to God alone, and
not to a fellow-mortal. This was the secret of guidance in the
trackless desert of old, and this is the secret of guidance in the vast
moral wilderness through which God's redeemed are passing now.
One man may say, Listen to me; and another may say, Listen to me;
and a third may say, Let each one take his own way. The obedient
heart says, in opposition to all, I must follow my Lord.
This makes all so simple. It will not, by any means, tender to foster
a spirit of haughty independence; quite the reverse. The more I am
taught to lean on God alone for guidance, the more I shall distrust
and look off from myself; and this, assuredly, is not independence.
True, it will deliver me from servile following of any man, by giving
me to feel my responsibility to Christ alone; but this is precisely what
is so much needed at the present moment. The more closely we
examine the elements that are abroad in the professing Church, the
more we shall be convinced of our personal need of this entire
subjection to divine authority, which is only another name for "the
fear of the Lord," or, "a single eye." There is one brief sentence, in
the opening of the Acts of the Apostles, which furnishes a perfect
antidote to the self-will and the servile fear of man so rife around us,
and that is, "We must obey God." What an utterance! "We must
obey." This is the cure for self-will. "We must obey God." This is the
cure for servile subjection to the commandments and doctrines of
men. There must be obedience; but obedience to what? To God's

authority, and to that alone. Thus the soul is preserved from the
influence of infidelity on the one hand, and superstition on the other.
Infidelity says, Do as you like. Superstition says, Do as man tells
you. Faith says, "We must obey God."
Here is the holy balance of the soul in the midst of the conflicting
and confounding influences around us in this our day. As a servant, I
am to obey my Lord; as a child, I am to hearken to my Father's
commandments. Nor am I the less to do this although my fellow-
servants and my brethren may not understand me. I must
remember that the immediate business of my soul is with God
Himself.—
"He before whom the elders bow,
With Him is all my business now."
It is my privilege to be as sure that I have my Master's mind as to
my path as that I have His Word for the security of my soul. If not,
where am I? Is it not my privilege to have a single eye? Yes, surely.
And what then? "A body full of light." Now, if my body is full of light,
can my mind be full of perplexity? Impossible. The two things are
wholly incompatible; and hence, when one is plunged "in dark
uncertainty," it is very plain his eye is not single. He may seem very
sincere, he may be very anxious to be guided aright; but he may
rest assured there is the lack of a single eye—that indispensable
prerequisite to divine guidance. The Word is plain,—"If thine eye is
single, thy whole body also is full of light." God will ever guide the
obedient, humble soul; but, on the other hand, if we do not walk
according to the light communicated, we shall get into darkness.
Light not acted upon becomes darkness, and oh, "how great is that
darkness!" Nothing is more dangerous than tampering with the light
which God gives. It must, sooner or later, lead to the most
disastrous consequences. "Take heed, therefore, that the light which
is in thee be not darkness." "Hear, ye, and give ear: be not proud;
for the Lord hath spoken. Give glory to the Lord your God, before He
cause darkness, and before your feet stumble on the dark

mountains, and while ye look for light, He turn it into the shadow of
death, and make it gross darkness." (Jer. xiii. 15, 16.)
This is deeply solemn. What a contrast between a man having a
single eye, and a man not acting on the light which God has given
him! The one has his body full of light; the other has his body full of
darkness: the one has no part dark; the other is plunged in gross
darkness: the one is a light-bearer for others; the other is a
stumbling-block in the way. We know nothing more solemn than the
judicial acting of God, in actually turning our light into darkness,
because we have refused to act on the light which He has been
pleased to impart.
Christian reader, art thou acting up to thy light? Has God sent a ray
of light into thy soul? Has He shown thee something wrong in thy
ways or associations? Art thou persisting in any line of action which
conscience tells thee is not in full accordance with thy Master's will?
Search and see. "Give glory to the Lord thy God." Act on the light.
Do not hesitate. Think not of consequences. Obey, we beseech thee,
the word of thy Lord. This very moment, as thine eye scans these
lines, let the purpose of thy soul be to depart from iniquity wherever
thou findest it. Say not, Whither shall I go? What shall I do next?
There is evil everywhere. It is only escaping from one evil to plunge
into another. Say not these things; do not argue or reason; do not
look at results; think not of what the world or the world-church will
say of thee; rise above all these things, and tread the path of light—
that path which shineth more and more unto the perfect day of
glory. Remember, God never gives light for two steps at a time. If He
has given thee light for one step, then, in the fear and love of His
Name, take that one step, and thou wilt assuredly get more light—
yes, "more and more." But if there be the refusal to act, the light
which is in thee will become gross darkness, thy feet will stumble on
the dark mountains of error which lie on either side of the straight
and narrow path of obedience; and thou wilt become a stumbling-
block in the path of others. Some of the most grievous stumbling-
blocks that lie, at this moment, in the pathway of anxious inquirers

are found in the persons of those who once seemed to possess the
truth, but have turned from it. The light which was in them has
become darkness, and oh, how great and how appalling is that
darkness! How sad it is to see those who ought to be light-bearers,
acting as a positive hindrance to young and earnest Christians! But
let not young Christians be hindered by them. The way is plain. "The
fear of the Lord, that is wisdom; and to depart from evil is
understanding." Let each one hear and obey for himself the voice of
the Lord. "My sheep hear My voice, and I know them, and they
follow Me." The Lord be praised for this precious word! It puts each
one in the place of direct responsibility to Christ Himself; it tells us
plainly what is God's way, and, just as plainly, how to find it.
C. H. M.

THE UNEQUAL YOKE
No one who sincerely desires to attain, in his own person, or
promote in others, a purer and more elevated discipleship, can
possibly contemplate the Christianity of the present day without an
indescribable feeling of sadness and heaviness. Its tone is so
excessively low, its aspect so sickly, and its spirit so enfeebled, that
one is, at times, tempted to despair of any thing like a true and
faithful witness for an absent Lord. All this is the more truly
deplorable when we remember the commanding motives by which it
is our special privilege ever to be actuated. Whether we look at the
Master whom we are called to follow, the path which we are called
to tread, the end which we are called to keep in view, or the hopes
by which we are to be animated, we cannot but own that, were all
these entered into and realized by a more simple faith, we should
assuredly exhibit a more ardent discipleship. "The love of Christ,"
says the apostle, "constraineth us." This is the most powerful motive
of all. The more the heart is filled with Christ's love, and the eye
filled with His blessed person, the more closely shall we seek to
follow in His heavenly track. His footmarks can only be discovered by
"a single eye;" and unless the will is broken, the flesh mortified, and
the body kept under, we shall utterly fail in our discipleship, and
make shipwreck of faith and a good conscience.
Let not my reader misunderstand me. It is not here, by any means,
a question of personal salvation. It is quite another thing. Nothing
can be more basely selfish than, having received salvation as the
fruit of Christ's agony and bloody sweat, His cross and passion, to
keep at as great a distance from His sacred person as we can
without forfeiting our personal safety. This is, even in the judgment
of nature, deemed a character of selfishness worthy of unmingled
contempt; but when exhibited by one who professes to owe his
present and his everlasting all to a rejected, crucified, risen, and

absent, Master, no language can express its moral baseness.
"Provided I escape hell-fire, it makes little matter as to discipleship."
Reader, do you not, in your inmost soul, abhor this sentiment? If so,
then earnestly seek to flee from it, to the very opposite point of the
compass; and let your truthful language be, Provided that blessed
Master is glorified, it makes little matter, comparatively, about my
personal safety. Would to God that this were the sincere utterance of
many hearts in this day, when, alas, it may be too truly said that,
"All seek their own, not the things which are Jesus Christ's" (Phil. ii.
21). Would that the Holy Ghost would raise up, by His own resistless
power, and send forth, by His own heavenly energy, a band of
separated and consecrated followers of the Lamb, each one bound,
by the cords of love, to the horns of the altar—a company, like
Gideon's three hundred of old, able to confide in God and deny the
flesh. How the heart longs for this! How the spirit, bowed down at
times beneath the chilling and withering influence of a cold and
uninfluential profession, earnestly breathes after a more vigorous
and whole-hearted testimony for that One who emptied Himself and
laid aside His glory, in order that we, through His precious
bloodshedding, might be raised to companionship with Him in
eternal blessedness!
Now, amongst the numerous hindrances to this thorough
consecration of heart to Christ which I earnestly desire for myself
and my reader, "the unequal yoke" will be found to occupy a very
prominent place indeed. "Be ye not unequally yoked together
[ετεροζυγουντες] with unbelievers: for what partnership [μετοχη]
hath righteousness with unrighteousness [or rather lawlessness—
ανομια]? and what communion [κοινωνια] hath light with darkness?
And what concord hath Christ with Belial? or what part hath a
believer with an unbeliever [απιστου]? And what agreement hath the
temple of God with idols? for ye are the temple of the living God; as
God hath said, 'I will dwell in them, and walk in them; and I will be
their God, and they shall be My people.' 'Wherefore come out from
among them, and be ye separate, saith the Lord, and touch not the
unclean thing; and I will receive you, and will be a Father unto you,

and ye shall be My sons and daughters, saith the Lord Almighty.'" (2
Cor. vi. 14-18.)
Under the Mosaic economy, we learn the same moral principle.
—"Thou shalt not sow thy vineyard with divers seeds: lest the fruit
of thy seed which thou hast sown, and the fruit of thy vineyard, be
defiled. Thou shalt not plow with an ox and an ass together. Thou
shalt not wear a garment of divers sorts, as of woolen and linen
together." (Deut. xxii. 9-11; Lev. xix. 19.)
These scriptures will suffice to set forth the moral evil of an unequal
yoke. It may, with full confidence, be asserted that no one can be an
unshackled follower of Christ who is, in any way, "unequally yoked."
He may be a saved person, he may be a true child of God—a sincere
believer, but he cannot be a thorough disciple; and not only so, but
there is a positive hindrance to the full manifestation of that which
he may really be, notwithstanding his unequal yoke. "Come out, ...
and I will receive you, ... and ye shall be my sons and daughters,
saith the Lord Almighty." That is to say, Get your neck out of the
unequal yoke, and I will receive you, and there shall be the full,
public, practical manifestation of your relationship with the Lord
Almighty. The idea here is evidently different from that set forth in
James—"Of His own will begat He us, by the word of truth." And
also in Peter—"Being born again, not of corruptible seed, but of
incorruptible, by the Word of God, which liveth and abideth forever."
And again in 1 John—"Behold what manner of love the Father hath
bestowed upon us, that we should be called the sons of God." So
also in John's gospel—"But as many as received Him, to them gave
He power to become the sons of God, even to them that believe on
His name; which were born, not of blood, nor of the will of the flesh,
nor of the will of man, but of God." In all these passages, the
relationship of sons is founded upon the divine counsel and the
divine operation, and is not set before us as the consequence of any
acting of ours; whereas in 2 Corinthians vi. it is put as the result of
our getting out of the unequal yoke. In other words, it is entirely a
practical question. Thus in Matthew v. we read, "But I say unto you,

'Love your enemies, bless them that curse you, do good to them
that hate you, and pray for them which despitefully use you, and
persecute you; in order that [οπως] ye may be the sons of your
Father which is in heaven; because He causeth His sun to rise upon
the evil and the good, and sendeth rain upon the just and the
unjust." Here too it is the practical establishment and public
declaration of the relationship, and its moral influence. It becomes
the sons of such a Father to act in such a way. In short, we have the
abstract position or relationship of sons founded on God's sovereign
will and operation; and we have the moral character consequent
upon and flowing out of this relationship which affords just ground
for God's public acknowledgment thereof. God cannot fully and
publicly own those who are unequally yoked together with
unbelievers, for, were He to do so, it would be an acknowledgment
of the unequal yoke. He cannot acknowledge "darkness,"
"unrighteousness," "Belial," "idols," and "an infidel." How could He?
Hence, if I yoke myself with any of these, I am morally and publicly
identified with them, and not with God at all. I have put myself into
a position which God cannot own, and, as a consequence, He cannot
own me; but if I withdraw myself from that position—if I "come out
and be separate"—if I take my neck out of the unequal yoke—then,
but not until then, can I be publicly and fully received and owned as
a "son or daughter of the Lord Almighty."
This is a solemn and searching principle for all who feel that they
have unhappily gotten themselves into such a yoke. They are not
walking as disciples, nor are they publicly or morally on the ground
of sons. God cannot own them. Their secret relationship is not the
point; but they have put themselves thoroughly off God's ground.
They have foolishly thrust their neck into a yoke which, inasmuch as
it is not Christ's yoke, must be Belial's yoke; and until they cast off
that yoke, God cannot own them as His sons and daughters. God's
grace, no doubt, is infinite, and can meet us in all our failure and
weakness; but if our souls aspire after a higher order of discipleship,
we must at once cast off the unequal yoke, cost what it may; that is,
if it can be cast off; but if it cannot, we must only bow our heads

beneath the shame and sorrow thereof, looking to God for full
deliverance.
Now, there are four distinct phases in which "the unequal yoke" may
be contemplated, viz, the domestic, the commercial, the religious,
and the philanthropic. Some may be disposed to confine 2
Corinthians vi. 14 to the first of these; but the apostle does not so
confine it. The words are, "Be not unequally yoked together with
unbelievers." He does not specify the character or object of the
yoke, and therefore we are warranted in giving the passage its
widest application, by bringing its edge to bear directly upon every
phase of the unequal yoke; and we shall see the importance of so
doing ere we close these remarks, if the Lord permit.
I. And first, then, let us consider the domestic or marriage yoke.
What pen can portray the mental anguish, the moral misery,
together with the ruinous consequences as to spiritual life and
testimony, flowing from a Christian's marriage with an unconverted
person? I suppose nothing can be more deplorable than the
condition of one who discovers, when it is too late, that he has
linked himself for life with one who cannot have a single thought or
feeling in common with him. One desires to serve Christ; the other
can only serve the devil: one breathes after the things of God; the
other sighs for the things of this present world: the one earnestly
seeks to mortify the flesh, with all its affections and desires; the
other only seeks to minister to and gratify these very things. Like a
sheep and a goat linked together, the sheep longs to feed on the
green pasture in the field, while, on the other hand, the goat craves
the brambles which grow in the ditch. The sad consequence is that
both are starved. One will not feed on the pasture, and the other
cannot feed upon the brambles, and thus neither gets what his
nature craves, unless the goat, by superior strength, succeeds in
forcing his unequally yoked companion to remain among the
brambles, there to languish and die.
The moral of this is plain enough; and, moreover, it is, alas! of but
too common occurrence. The goat generally succeeds in gaining his

end. The worldly partner carries his or her point, in almost every
instance. It will be found, almost without exception, that in cases of
the unequal marriage-yoke, the poor Christian is the sufferer, as is
evidenced by the bitter fruits of a bad conscience, a depressed
heart, a gloomy spirit, and a desponding mind. A heavy price, surely,
to pay for the gratification of some natural affection, or the
attainment, it may be, of some paltry worldly advantage. In fact, a
marriage of this kind is the death-knell of practical Christianity, and
of progress in the divine life. It is morally impossible that any one
can be an unfettered disciple of Christ with his neck in the marriage-
yoke with an unbeliever. As well might a racer in the Olympic or
Isthmæan games have expected to gain the crown of victory by
attaching a heavy weight or dead body to his person. It is enough,
surely, to have one dead body to sustain, without attaching another.
There never was a true Christian yet who did not find that he had
abundant work to do in endeavoring to grapple with the evils of one
heart, without going to burden himself with the evils of two; and,
without doubt, the man who foolishly and disobediently marries an
unconverted woman; or the woman who marries an unconverted
man, is burdened with the combined evils of two hearts; and who is
sufficient for these things? One can most fully count upon the grace
of Christ for the subjugation of his own evil nature: but he certainly
cannot count, in the same way, upon that grace in reference to the
evil nature of his unequal yoke-fellow. If he have yoked himself
ignorantly, the Lord will meet him personally, on the ground of full
confession, with entire restoration of soul, but in the matter of his
discipleship, he will never recover it.
Now, in considering the terribly evil consequences of the unequal
marriage-yoke, it is mainly as bearing upon our discipleship that we
are looking at them. I say "mainly" because our entire character and
experience are deeply affected thereby. I very much question if any
one can give a more effectual blow to his prosperity in the divine life
than by assuming an unequal yoke. Indeed, the very fact of so doing
proves that spiritual decline has already set in, with most alarming
symptoms; but as to his discipleship and testimony, the lamp thereof

may be regarded as all but gone out; or if it does give an occasional
faint glimmer, it only serves to make manifest the awful gloom of his
unhappy position, and the appalling consequences of being
"unequally yoked together with an unbeliever."
Thus much as to the question of the unequal yoke in its influence
upon the life, the character, the testimony, and the discipleship of
the child of God.
I would now say a word as to its moral effect as exhibited in the
domestic circle. Here too the consequences are truly melancholy. Nor
could they possibly be otherwise. Two persons have come together
in the closest and most intimate relationship, with tastes, habits,
feelings, desires, tendencies, and objects diametrically opposite.
They have nothing in common; so that in every movement they can
but grate one against the other. The unbeliever cannot, in reality, go
with the believer; and if there should, through excessive amiability
or downright hypocrisy, be a show of acquiesence, what is it worth
in the sight of the Lord, who judges the true state of the heart in
reference to Himself? But little indeed; yea, it is worse than
worthless. Then, again, if the believer should unhappily go in any
measure with his unequal yoke-fellow, it can only be at the expense
of his discipleship, and the consequence is, a condemning
conscience in the sight of the Lord; and this, again, leads to
heaviness of spirit, and, it may be, sourness of temper in the
domestic circle, so that the grace of the gospel is by no means
commended, and the unbeliever is not attracted or won. Thus it is in
every way most sorrowful. It is dishonoring to God, destructive of
spiritual prosperity, utterly subversive of discipleship and testimony,
and entirely hostile to domestic peace and blessing. It produces
estrangement, coldness, distance, and misunderstanding: or, if it
does not produce these, it will doubtless lead, on the part of the
Christian, to a forfeiture of his discipleship and his good conscience,
both of which he may be tempted to offer as a sacrifice upon the
altar of domestic peace. Thus, whatever way we look at it, an
unequal yoke must lead to the most deplorable consequences.

Then, as to its effect upon children, it is equally sad. These are
almost sure to flow in the current with the unconverted parent.
"Their children spoke half in the speech of Ashdod, and could not
speak in the Jews' language, but according to the language of each
people." There can be no union of heart in the training of the
children,—no joint and mutual confidence in reference to them. One
desires to bring them up in the nurture and admonition of the Lord;
the other desires to bring them up in the principles of the world, the
flesh, and the devil: and as all the sympathies of the children, as
they grow up, are likely to be ranged on the side of the latter, it is
easy to see how it will end. In short, it is an unseemly, unscriptural,
and vain effort to plow with an "unequal yoke," or to "sow the
ground with mingled seed;" and all must end in sorrow and
confusion.[18]
I shall, ere turning from this branch of our subject, offer a remark as
to the reasons which generally actuate Christians in the matter of
entering into the unequal marriage-yoke. We all know, alas! how
easily the poor heart persuades itself of the rightness of any step
which it desires to take, and how the devil furnishes plausible
arguments to convince us of its rightness—arguments which the
moral condition of the soul causes us to regard as clear, forcible, and
satisfactory. The very fact of our thinking of such a thing, proves our
unfitness to weigh, with a well-balanced mind and spiritually
adjusted conscience, the solemn consequences of such a step. If the
eye were single (that is, if we were governed but by one object,
namely, the glory and honor of the Lord Jesus Christ), we should
never entertain the idea of putting our necks in an unequal yoke;
and consequently we should have no difficulty or perplexity about
the matter. A racer, whose eye was resting on the crown, would not
be troubled with any perplexity as to whether he ought to stop and
tie a hundred-weight round his neck. Such a thought would never
cross his mind: and not only so, but a thorough racer would have a
distinct and almost intuitive perception of every thing which would
be likely to prove a hindrance to him in running the race; and, of

course, with such an one, to perceive would be to reject with
decision.[19]
Now, were it thus with Christians in the matter of unscriptural
marriage, it would save them a world of sorrow and perplexity; but it
is not thus. The heart gets out of communion, and is morally
incompetent to "try the things that differ;" and when in this
condition, the devil gains an easy conquest, and speedy success in
his wicked effort to induce the believer to yoke himself with
"Belial"—with "unrighteousness"—with "darkness"—with "an infidel."
When the soul is in full communion with God, it is entirely subject to
His Word; it sees things as He sees them, calls them what He calls
them, and not what the devil or his own carnal heart would call
them. In this way, the believer escapes the insnaring influence of a
deception which is very frequently brought to bear upon him in this
matter, namely, a false profession of religion on the part of the
person whom he desires to marry. This is a very common case. It is
easy to show symptoms of leaning toward the things of God; and
the heart is treacherous and base enough to make a profession of
religion in order to gain its end; and not only so, but the devil, who
is "transformed into an angel of light," will lead to this false
profession, in order thereby the more effectually to entrap the feet
of a child of God. Thus it comes to pass that Christians, in this
matter, suffer themselves to be satisfied, or at least profess
themselves satisfied, with evidence of conversion which under any
other circumstances they would regard as utterly lame and flimsy.
But, alas! experience soon opens the eyes to the reality. It is
speedily discovered that the profession was all a vain show, that the
heart is entirely in and of the world. Terrible discovery. Who can
detail the bitter consequences of such a discovery—the anguish of
heart—the bitter reproaches and cuttings of conscience—the shame
and confusion—the loss of power and blessing—the forfeiture of
spiritual peace and joy—the sacrifice of a life of usefulness? Who can
describe all these things? The man awakes from his delusive dream,
and opens his eyes upon the tremendous reality that he is yoked for

life with "Belial"! Yes, this is what the Spirit calls it. It is not an
inference, or a deduction arrived at by a process of reasoning; but a
plain and positive statement of holy Scripture, that thus the matter
stands in reference to one who, from whatever motive, or under the
influence of whatever reasons, or deceived by whatever false
pretences, has entered into an unequal marriage-yoke.
Oh, my beloved Christian reader, if you are in danger of entering into
such a yoke, let me earnestly, solemnly, and affectionately entreat of
you to pause first, and weigh the matter in the balances of the
sanctuary, ere you move forward a single hair's breadth on such a
fatal path! You may rest assured that you will no sooner have taken
the step than your heart will be assailed by hopeless regrets, and
your life embittered by unnumbered sorrows. Let nothing induce you
to yoke yourself with an unbeliever. Are your affections engaged? Then,
remember, they cannot be the affections of your new man; they are,
be assured of it, those of the old or carnal nature, which you are
called upon to mortify and set aside. Wherefore you should cry to
God for spiritual power to rise above the influence of such affections;
yea, to sacrifice them to Him. Again, are your interests concerned?
Then remember that they are only your interests; and if they are
promoted, Christ's interests are sacrificed by your yoking yourself
with "Belial." Furthermore, they are only your temporal, and not your
eternal interests. In point of fact, the interests of the believer and
those of Christ ought to be identical; and it is plain that His interests,
His honor, His truth, His glory, must inevitably be sacrificed if a
member of His body is linked with "Belial." This is the true way to
look at the question. What are a few hundreds, or a few thousands,
to an heir of heaven? "God is able to give thee much more than
this." Are you going to sacrifice the truth of God, as well as your
own spiritual peace, prosperity, and happiness, for a paltry trifle of
gold, which must perish in the using of it? Ah, no! God forbid! Flee
from it, as a bird from the snare which it sees and knows. Stretch
out the hand of genuine, well-braced, whole-hearted discipleship,
and take the knife and slay your affections and your interests on the
altar of God, and then, even though there should not be an audible

voice from heaven to approve your act, you will have the invaluable
testimony of an approving conscience and an ungrieved Spirit—an
ample reward, surely, for the most costly sacrifice which you can
make. May the Spirit of God give power to resist Satan's
temptations.
It is hardly needful to remark here that in cases where conversion
takes place after marriage, the complexion of the matter is very
materially altered. There will then be no smitings of conscience, for
example, and the whole thing is modified in a variety of particulars.
Still, there will be difficulty, trial, and sorrow, unquestionably. The
only thing is, that one can far more happily bring the trial and
sorrow into the Lord's presence, when he has not deliberately and
willfully plunged himself thereinto; and, blessed be God, we know
how ready He is to forgive, restore, and cleanse from all
unrighteousness the soul that makes full confession of its error and
failure. This may comfort the heart of one who has been brought to
the Lord after marriage. Moreover, to such an one the Spirit of God
has given specific direction and blessed encouragement in the
following passage: "If any brother have an unbelieving wife, and she
think proper to dwell with him, let him not put her away: and if any
woman have an unbelieving husband, and he think proper to dwell
with her, let her not put him away (for the unbelieving husband is
sanctified by the wife, and the unbelieving wife is sanctified by the
husband, else were your children unclean, but now are they holy)....
For what knowest thou, O wife, if thou shalt save thy husband? or
what knowest thou, O husband, if thou shalt save thy wife?" (1 Cor.
vii. 12-16.)
II. We shall now consider "the unequal yoke" in its commercial
phase, as seen in cases of partnership in business. This, though not
so serious an aspect of the yoke as that which we have just been
considering, will nevertheless be found a very positive barrier to the
believer's testimony. When a Christian yokes himself, for business
purposes, with an unbeliever—whether that unbeliever be a relative
or not—or when he becomes a member of a worldly firm, he

virtually surrenders his individual responsibility. Henceforth the acts
of the firm become his acts, and it is perfectly out of the question to
think of getting a worldly firm to act on heavenly principles. They
would laugh at such a notion, inasmuch as it would be an effectual
barrier to the success of their commercial schemes. They will feel
perfectly free to adopt a number of expedients in carrying on their
business which would be quite opposed to the spirit and principles of
the kingdom in which he is, and of the Church of which he forms a
part. Thus he will find himself constantly in a most trying position.
He may use his influence to Christianize the mode of conducting
affairs, but they will compel him to do business as others do, and he
has no remedy save to mourn in secret over his anomalous and
difficult position, or else to go out at great pecuniary loss to himself
and family. Where the eye is single, there will be no hesitation as to
which of these alternatives to adopt; but, alas! the very fact of
getting into such a position proves the lack of a single eye; and the
fact of being in it argues the lack of spiritual capacity to appreciate
the value and power of the divine principles which would infallibly
bring a man out of it. A man whose eye was single could not
possibly yoke himself with an unbeliever for the purpose of making
money. Such an one could only set, as an object before his mind,
the direct glory of Christ; and this object could never be gained by a
positive transgression of divine principle.
This makes it very simple. If it does not glorify Christ for a Christian
to become a partner in a worldly firm, it must, without doubt, further
the designs of the devil. There is no middle ground; but that it does
not glorify Christ is manifest, for His Word says, "Be not unequally
yoked together with unbelievers." Such is the principle, which cannot
be infringed without damage to the testimony, and forfeiture of
spiritual blessing. True, the conscience of a Christian who
transgresses in this matter may seek relief in various ways—may
have recourse to various subterfuges—may set forth various
arguments to persuade itself that all is right. It will be said that "we
can be very devoted and very spiritual, so far as we are personally
concerned, even though we are yoked, for business purposes, with

an unbeliever." This will be found fallacious when brought to the test
of the actual practice. A servant of Christ will find himself hampered
in a hundred ways by his worldly partnership. If in matters of service
to Christ he is not met with open hostility, he will have to encounter
the enemy's secret and constant effort to damp his ardor, and throw
cold water on all his schemes. He will be laughed at and despised—
he will be continually reminded of the effect which his enthusiasm
and fanaticism will produce in reference to the business prospects of
the firm. If he uses his time, his talents, or his pecuniary resources
in what he believes to be the Lord's service, he will be pronounced a
fool or a madman, and reminded that the true—the proper way for a
commercial man to serve the Lord is to "attend to business, and
nothing but business;" and that it is the exclusive business of
clergymen and ministers to attend to religious matters, inasmuch as
they are set apart and paid for so doing.
Now, although the Christian's renewed mind may be thoroughly
convinced of the fallacy of all this reasoning—although he may see
that this worldly wisdom is but a flimsy, threadbare cloak, thrown
over the heart's covetous practices—yet who can tell how far the
heart may be influenced by such things? We get weary of constant
resistance. The current becomes too strong for us, and we gradually
yield ourselves to its action, and are carried along on its surface.
Conscience may have some death-struggles; but the spiritual
energies are paralyzed, and the sensibilities of the new nature are
blunted, so that there is no response to the cries of conscience, and
no effectual effort to withstand the enemy; the worldliness of the
Christian's heart leagues itself with the opposing influences from
without—the outworks are stormed, and the citadel of the soul's
affections vigorously assaulted; and finally, the man settles down in
thorough worldliness, exemplifying in his own person the prophet's
touching lament, "Her Nazarites were purer than snow, they were
whiter than milk, they were more ruddy in body than rubies, their
polishing was of sapphire: their visage is blacker than a coal; they
are not known in the streets; their skin cleaveth to their bones; it is
withered, it is become like a stick." (Lam. iv. 7, 8.) The man who was

once known as a servant of Christ—a fellow-helper unto the kingdom
of God—making use of his resources only to further the interests of
the gospel of Christ, is now, alas! settled down upon his lees, only
known as a plodding, keen, bargain-making man of business, of
whom the apostle might well say, "Demas hath forsaken me, having
loved this present age [τον νυν αιωνα]."
But perhaps nothing so operates on the hearts of Christians, in
inducing them to yoke themselves commercially with unbelievers, as
the habit of seeking to maintain the two characters of a Christian
and a man of business. This is a grievous snare. In point of fact,
there can be no such thing. A man must be either the one or the
other. If I am a Christian, my Christianity must show itself as a living
reality in that in which I am; and if it cannot show itself there, I
ought not to be there: for if I continue in a sphere or position in
which the life of Christ cannot be manifested, I shall speedily
possess naught of Christianity but the name without the reality—the
outward form without the inward power—the shell without the
kernel. I should be the servant of Christ, not merely on Sunday, but
from Monday morning to Saturday night. I should not only be a
servant of Christ in the public assembly, but also in my place of
business, whatever it may happen to be. But I cannot be a proper
servant of Christ with my neck in the yoke with an unbeliever; for
how could the servants of two hostile masters work in the same
yoke? It is utterly impossible; as well might one attempt to link the
sun's meridian beams with the profound darkness of midnight. It
cannot be done; and I do therefore most solemnly appeal to my
reader's conscience, in the presence of Almighty God, who shall
judge the secrets of men's hearts by Jesus Christ, as to this
important matter. I would say to him, if he is thinking of getting into
partnership with an unbeliever, Flee from it! yes, flee from it, though
it promises you the gain of thousands. You will plunge yourself into a
mass of sorrow and trouble. You are going to "plow" with one whose
feelings, instincts, and tendencies are diametrically opposed to your
own. "An ox and an ass" are not so unlike, in every respect, as a
believer and an unbeliever. How will you ever get on? He wants to

make money—to profit himself—to get on in the world; you want (at
least you ought to want) to grow in grace and holiness—to advance
the interests of Christ and His gospel on the earth, and to push
onward to the everlasting kingdom of the Lord Jesus Christ. His
object is money; yours, I trust, is Christ: he lives for this world; you,
for the world to come; he is engrossed with the things of time; you,
with those of eternity. How, then, can you ever take common ground
with him? Your principles, your motives, your objects, your hopes,
are all opposed. How is it possible you can get on? How can you
have aught in common? Surely, all this needs only to be looked at
with a single eye in order to be seen in its true light. It is impossible
that any one whose eye is filled and whose heart is occupied with
Christ, could ever yoke himself with a worldly partner, for any object
whatsoever. Wherefore, my beloved Christian reader, let me once
more entreat you, ere you take such a tremendous step—a step
fraught with such awful consequences—so pregnant with danger to
your best interests, as well as to the testimony of Christ, with which
you are honored—to take the whole matter, with an honest heart,
into the sanctuary of God, and weigh it in His sacred balance. Ask
Him what He thinks of it, and hearken, with a subject will and a
well-adjusted conscience, to His reply. It is plain and powerful—yea,
as plain and as powerful as though it fell from the open heavens
—"Be not unequally yoked together with unbelievers."
But if, unhappily, my reader is already in the yoke, I would say to
him, disentangle yourself as speedily as you can. I am much
mistaken if you have not already found the yoke a burdensome one.
To you it were superfluous to detail the sad consequences of being
in such a position; you doubtless know them all. It is needless to
print them on paper, or paint them on canvas, to one who has
entered into all their reality. My beloved brother in Christ, lose not a
moment in seeking to throw off the yoke. This must be done before
the Lord, on His principles, and by His grace. It is easier to get into a
wrong position than to get out of it. A partnership of ten or twenty
years' standing cannot be dissolved in a moment. It must be done
calmly, humbly, and prayerfully, as in the sight of the Lord, and with

entire reference to His glory. I may dishonor the Lord as much in my
way of getting out of a wrong position as by getting into it at the
first. Hence, if I find myself in partnership with an unbeliever, and
my conscience tells me I am wrong, let me honestly and frankly
state to my partner that I can no longer go on with him; and having
done that, my place is to use every exertion to wind up the affairs of
the firm in an upright, a straightforward, and businesslike manner, so
as to give no possible occasion to the adversary to speak
reproachfully, and that my good may not be evil spoken of. We must
avoid rashness, headiness, and high-mindedness, when apparently
acting for the Lord, and in defense of His holy principles. If a man
gets entangled in a net, or involved in a labyrinth, it is not by bold
and violent plunging he will extricate himself. No; he must humble
himself, confess his sins before the Lord, and then retrace his steps,
in patient dependence upon that grace which can not only pardon
him for being in a wrong position, but lead him forth into a right
one.
Moreover, as in the case of the marriage-yoke, the matter is very
much modified by the fact of the partnership having been entered
into previous to conversion. Not that this would, in the slightest
degree, justify a continuance in it. By no means; but it does away
with much of the sorrow of heart and defilement of conscience
connected with such a position, and will also very materially affect
the mode of escape therefrom. Besides, the Lord is glorified by, and
He assuredly accepts, the moral bent of the heart and conscience in
the right direction. If I judge myself for being wrong, and that the
moral bent of my heart and conscience is to get right, God will
accept of that, and surely set me right. But if He sets me right, He
will not suffer me to do violence to one truth while seeking to act in
obedience to another. The same Word that says "Be not unequally
yoked together with unbelievers" says also "Render therefore to all
their dues"—"owe no man any thing"—"provide things honest in the
sight of all"—"walk honestly toward them that are without." If I have
wronged God by getting into partnership with an unbeliever, I must
not wrong any man in my way of getting out of it. Profound

subjection to the Word of God, by the power of the Holy Ghost, will
set all to rights, will lead us into straight paths, and enable us to
avoid all dangerous extremes.
III. In glancing for a moment at the religious phase of the unequal
yoke, I would assure my reader that it is by no means my desire to
hurt the feelings of any one by canvassing the claims of the various
denominations around me. Such is not my purpose. The subject of
this paper is one of quite sufficient importance to prevent its being
encumbered by the introduction of other matters. Moreover, it is too
definite to warrant any such introduction. "The unequal yoke" is our
theme, and to it we must confine our attention.
In looking through Scripture we find almost numberless passages
setting forth the intense spirit of separation which ought ever to
characterize the people of God. Whether we direct our attention to
the Old Testament, in which we have God's relationship and dealings
with His earthly people, Israel, or to the New Testament, in which
we have His relationship and dealings with His heavenly people, the
Church, we find the same truth prominently set forth, namely, the
entire separation of those who belong to God. Israel's position is
thus stated in Balaam's parable, "Lo, the people shall dwell alone,
and shall not be reckoned amongst the nations." Their place was
outside the range of all the nations of the earth, and they were
responsible to maintain that separation. Throughout the entire
Pentateuch they were instructed, warned, and admonished as to
this; and throughout the psalms and the prophets we have a record
of their failure in the maintenance of this separation, which failure,
as we know, has brought down upon them the heavy judgments of
the hand of God. It would swell this little paper into a volume were I
to attempt a quotation of all the passages in which this point is put
forward. I take it for granted that my reader is sufficiently
acquainted with his Bible, to render such quotations unnecessary.
Should he not be so, however, a reference, in his concordance, to
the words, "separate," "separated," and "separation" will suffice to
lay before him at a glance the body of Scripture-evidence on the

subject. The passage just quoted from the book of Numbers is the
expression of God's thoughts about His people Israel: "The people
shall dwell ALONE."
The same is true, only upon a much higher ground, in reference to
God's heavenly people, the Church—the body of Christ—composed
of all true believers. They too are a separated people.
We shall now proceed to examine the ground of this separation.
There is a great difference between being separate on the ground of
what we are and of what God is. The former makes a man a
Pharisee; the latter makes him a saint. If I say to a poor fellow-
sinner, "Stand by thyself, I am holier than thou," I am a detestable
Pharisee and a hypocrite; but if God, in His infinite condescension
and perfect grace, says to me, I have brought you into relationship
with Myself in the person of My Son Jesus Christ, therefore be
separate and holy from all evil; come out from among them and be
separate; I am bound to obey, and my obedience is the practical
manifestation of my character as a saint—a character which I have,
not because of any thing in myself, but simply because God has
brought me near unto Himself through the precious blood of Christ.
It is well to be clear as to this. Pharisaism and divine sanctification
are two very different things; and yet they are often confounded.
Those who contend for the maintenance of that place of separation
which belongs to the people of God, are constantly accused of
setting themselves up above their fellow-men, and of laying claim to
a higher degree of personal sanctity than is ordinarily possessed.
This accusation arises from not attending to the distinction just
referred to. When God calls upon men to be separate, it is on the
ground of what He has done for them upon the cross, and where He
has set them, in eternal association with Himself, in the person of
Christ. But if I separate myself on the ground of what I am in myself,
it is the most senseless and vapid assumption, which will sooner or
later be made manifest. God commands His people to be holy on the
ground of what He is: "Be ye holy, for I am holy." This is evidently a
very different thing from "Stand by thyself: I am holier than thou." If

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