And the Lord said, etc. Now that Moses had at last given up his own will and entered on the path of obedience, God comforted him with a fresh revelation,, and gave him fresh instructions as to what exactly he was to say to Pharaoh.
The statements of Exodus 4:21 are not new, being anticipated in Exodus 3:19-20; but the directions in Exodus 3:22 -23 are wholly new, and point to the greatest of all the miracles wrought in Egypt—the death of the firstborn.