18 So Moses went back home to Jethro, his father-in-law. "Please let me return to my relatives in Egypt," Moses said. "I don't even know if they are still alive." "Go in peace," Jethro replied. 19 Before Moses left Midian, the Lord said to him, "Return to Egypt, for all those who wanted to kill you have died." 20 So Moses took his wife and sons, put them on a donkey, and headed back to the land of Egypt. In his hand he carried the staff of God. 21 And the Lord told Moses, "When you arrive back in Egypt, go to Pharaoh and perform all the miracles I have empowered you to do. But I will harden his heart so he will refuse to let the people go. 22 Then you will tell him, 'This is what the Lord says: Israel is my firstborn son. 23 I commanded you, "Let my son go, so he can worship me." But since you have refused, I will now kill your firstborn son!'"
Matthew Henry's Commentary on Exodus 4:18-23
Commentary on Exodus 4:18-23
(Read Exodus 4:18-23)
After God had appeared in the bush, he often spake to Moses. Pharaoh had hardened his own heart against the groans and cries of the oppressed Israelites; and now God, in the way of righteous judgment, hardens his heart against the teaching of the miracles, and the terror of the plagues. But whether Pharaoh will hear, or whether he will forbear, Moses must tell him, Thus saith the Lord. He must demand a discharge for Israel, Let my son go; not only my servant, whom thou hast no right to detain, but my son. It is my son that serves me, and therefore must be spared, must be pleaded for. In case of refusal I will slay thy son, even thy first-born. As men deal with God's people, let them expect so to be dealt with.