In Exodus 3:1–4:31, Moses is called to lead the nation of Israel out of Egypt. Now a second call comes. Why? From Exodus 5:1–23 it becomes clear that Moses should not count on any assistance from Pharaoh, who will only make Israel’s slavery worse. Also, assistance cannot be expected from the people of Israel either, as they are only blaming Moses. And Moses complains that God does not fulfil his promises.
God makes clear that liberation only comes because of him. He repeats his promises and expands on them. (When God says things anew, it is never just a repeat of things; he always adds something new).
2 God spoke to Moses and said to him, “I am the LORD.