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.
Read Chapter 4
Augustine of Hippo
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.
Now let no one along with pagans or Manichaeans dare to censure or blame the justice of God. It is to be believed as most certain that not the violence of God but his own repeated wickedness and indomitable pride in opposition to God’s commands caused Pharaoh to become hardened. What does that mean which God said, “I will make him obstinate,” except that when my grace is withdrawn from him his own iniquity will harden him? In order that this may be known more clearly, we propose to your charity a comparison with visible things. As often as water is contracted by excessive cold, if the heat of the sun comes upon it, it becomes melted; when the same sun departs the water again becomes hard. Similarly the charity of many men freezes because of the excessive coldness of their sins, and they become as hard as ice; however, when the warmth of divine mercy comes upon them again, they are melted.
I shall harden Not by being the efficient cause of his sin; but by withdrawing from him, for his just punishment, the dew of grace, that might have softened his heart; and so suffering him to grow harder and harder. (Challoner)
Non impertiendo misericordiam. (St. Augustine, ep. 194, ad Sixt.) Thus God permitted the false miracles of the magicians, and did not suffer the scourges to continue long, so that the tyrant soon relapsed and forgot his promises. (Origen, Philos. xx; Theodoret in Rom. ix. 17.) (Calmet)
I shall harden: Not by being the efficient cause of his sin; but by withdrawing from him, for his just punishment, the dew of grace that might have softened his heart; and so suffering him to grow harder and harder.