You could say that these verses are superfluous; they provide no new information. But they function as a summary of what the Lord has said to Moses (Exodus 6:2–12).
God starts with, I am the LORD,
as he also started and ended his promises to Moses in Exodus 6:6–8. Moses protests, and then God encourages Moses and Aaron, as we read in Exodus 7:1–7.
28 On the day when the LORD spoke to Moses in the land of Egypt,