John Calvin Commentary Exodus 10:1

"And Jehovah said unto Moses, Go in unto Pharaoh: for I have hardened his heart, and the heart of his servants, that I may show these my signs in the midst of them," — Exodus 10:1 (ASV)

And the Lord said. Moses passes on to another plague, by which God took vengeance on the treachery and obstinacy of the wicked king; namely, that He handed over the remaining produce of the year, which He had spared, to be eaten and devoured by locusts. This was no ordinary punishment, to destroy Egypt by scarcity and famine, when all their grain had perished.

But, before Moses proceeds to this, he again relates that he was the proclaimer of this plague, and that God had announced to him the reason why Pharaoh had so often resisted to his own harm. Therefore God says that He had hardened his heart, so that He might display these miracles and evidences of His power. For if Pharaoh had been humbled and had yielded immediately, the contest would have been superfluous, since what would be the object of contending with a conquered and prostrate enemy?

The obstinacy of the tyrant, then, in so often provoking God, opened the way to more miracles, just as fire is produced by the collision of flint and iron. From this, the foolish notion is also refuted that Pharaoh's heart was hardened in no other way than by the miracles being set before his eyes. For Moses does not say that his heart was divinely hardened by the sight of the signs, but that it pleased God in this manner to manifest His power.

From this we also gather that whatever occurred was predestined by the sure counsel of God. For God willed to redeem His people in a unique and unusual way. So that this redemption might be more conspicuous and glorious, He set up Pharaoh against Himself like a rock, which by its hardness would provide an occasion for new and more remarkable miracles. Pharaoh was, therefore, hardened by the marvelous providence of God with this objective: that the grace of His deliverance might be neither contemptible nor obscure.

For God regarded His own people more than the Egyptians, as immediately appears: that you may tell in the ears of your son, and of your son’s son, etc. For far more abundant material for thanksgiving and for celebrating the memory of their deliverance was provided by the fact that the Israelites had seen God’s arm stretched forth so often from heaven, and with so many wonders.

Had they been redeemed by any ordinary method, the praise due to God would soon have been forgotten. It was proper, then, that their descendants should be thus instructed by their fathers, so that they might have no doubts as to the author of so illustrious a work. But it is here required of the fathers, who had been eyewitnesses of the signs, that they should be diligent and persistent in teaching their children; and upon these children also, care and attention in learning is urged, so that the recollection of God’s mercies should flourish throughout all ages. The practical effect of this doctrine is seen in Psalm 44 and Psalm 105.