When the Lord saw that he had turned aside to see, God called to him out of the bush, “Moses, Moses!” And he said, “Here I am.”
What an interesting interplay between God’s Sovereignty and human will. The angel, or an expression of God, calls out to Moses and then waits for his response. The text then makes a point to say that it was only after God saw Moses obey the call and come to him that he begins speaking his promises and showing his identity to Moses. God here shows patience, and waits for Moses.