God speaks to Moses from the burning bush
At Horeb, the mountain of God, a bush burned without burning up, and God called 80-year-old Moses to lead Israel out of Egypt.
God said to Moses, “I AM WHO I AM,” and he said, “You shall tell the children of Israel this: ‘I AM has sent me to you.’”
Exodus 3:14 (World English Bible)
God revealed himself as the God of Abraham, Isaac, and Jacob, who had seen his people's misery and come down to rescue them. When Moses asked his name, God answered, “I AM WHO I AM,” the meaning behind the name Yahweh. Jesus would later claim that name for himself (John 8:58).
Moses raised objection after objection. God gave him signs to perform and sent his brother Aaron to speak for him.
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Dating notes
Moses was 80 (Exodus 7:7; Acts 7:30). The location of Horeb, also called Mount Sinai, is debated: the traditional site is Jebel Musa in the southern Sinai Peninsula, while some place it in Midian, in northwest Arabia (compare Galatians 4:25).