And the LORD said unto Moses,
When you go
to return into Egypt, see that you do all those wonders before Pharaoh, whom I have put in your hand: but I will harden his heart, that he shall not let the people go.
All Commentaries on Exodus 4:21 Go To Exodus 4
Augustine of Hippo
AD 430
And you must not deny free will to Pharaoh just because God says in a number of places, “I have hardened Pharaoh” or “I will harden the heart of Pharaoh,” for it does not thereby follow that it was not Pharaoh himself that hardened his own heart. Furthermore, we read that this happened to Pharaoh after the plague of flies had been removed from the Egyptians, as the Scripture testifies: “And Pharaoh’s heart was hardened so that neither this time would he let the people go.” Thus it was that both God and Pharaoh caused this hardening of the heart: God, by his just judgments, Pharaoh, by his free will.