Moses was forty years old when he ran away from Egypt. He lived in the desert for forty more years and married Zipporah, the daughter of Jethro, the priest of Midian.
One day, he was herding his father-in-law’s sheep near Mt. Sinai, and the angel of the LORD appeared to him in flames of fire from within a bush. Moses saw that though the bush was on fire it did not burn up. So he went over to see this strange sight, and the Lord called to him from within the bush, "Moses! Moses!"
And Moses said, "Here I am."
"Do not come any closer," God said. "Take off your sandals, for the place where you are standing is holy ground. I am the God of your father, the God of Abraham, the God of Isaac, and the God of Jacob. I have seen the misery of my people in slavery in Egypt. I now plan to rescue them and bring them back to the land of the Canaanites, an abundant land flowing with milk and honey. So now, go. I am sending you to Pharaoh to bring my people, the Israelites, out of Egypt."
At this, Moses hid his face, because he was afraid to look at God. And he began arguing with Him. He said, "Who am I that I should go to Pharaoh and bring the Israelites out of Egypt? What if the Israelites do not believe me? And what if they ask who it is that sent me? What is his name?”
And God said to Moses, "I AM WHO I AM. This is what you are to say to the Israelites: ‘I AM has sent me to you.’” God also said to Moses, “I will be with you. As a sign that I have indeed sent you, I will bring you all back to this mountain to worship me after I've brought the people out of Egypt."
And God gave Moses two other signs to show the people to help them believe what he said. He said to Moses, “Throw down your shepherd’s staff.” Moses did, and it became a snake! Then God said, “Now pick it up by the tail.” When Moses picked it up, it became a staff again. God then told him to put his hand inside his robe. When he pulled it out, it was covered with leprosy, but when he put it back again it was healed. Then God said, “You will show to them these signs so they will believe that the Lord, the God of their fathers, has appeared to you.”
God also promised to send Moses’ brother Aaron with him. So Moses agreed and went back to Egypt.