One day Moses was taking care of Jethro’s flock. (Jethro was the priest of Midian and also Moses’ father-in-law.) When Moses led the flock to the west side of the desert, he came to Sinai, the mountain of God.
God said, “I will be with you. This will be the proof that I am sending you: After you lead the people out of Egypt, all of you will worship me on this mountain.”