1) Abraham built the Ka'ba in Mecca to show his love for one God. Mecca was an important religious and trading center because it contained the Ka'ba.
2) Muhammad was born in Mecca, which was a trading hub due to its many trade routes. After becoming orphaned, he worked as a trader and married Khadijah.
3) While meditating in a cave, Muhammad received his first revelation from the Angel Gabriel that he was to become God's prophet. His teachings were written down after his death in the Quran.