Exodus 9:35

The prayer of Moses opened and shut heaven, like Elias's ( Jam. v. 17, 18 ), and such is the power of God's two witnesses ( Rev. xi. 6 ); yet neither Moses nor Elias, nor those two witnesses, could subdue the hard hearts of men. Pharaoh was frightened into a compliance by the judgment, but, when it was over, his convictions vanished, and his fair promises were forgotten.

And the heart of Pharaoh was hardened,.... Instead of being softened, as it seemed to be when under the plague, it became harder and harder when delivered from it: neither would he let the children of Israel go; though he had so absolutely promised it, and assured them that he would not keep them, and that they should not stay any longer: as the Lord had spoken by Moses; that so his heart would be hardened until the signs and wonders were multiplied upon him, God designed to perform, Exo 4:21.

And the heart of Pharaoh was hardened - In consequence of his sinning yet more, and hardening his own heart against both the judgments and mercies of God, we need not be surprised that, after God had given him the means of softening and repentance, and he had in every instance resisted and abused them, he should at last have been left to the hardness and darkness of his own obstinate heart, so as to fill up the measure of his iniquity, and rush headlong to his own destruction. In the fifth, sixth, and seventh plagues described in this chapter, we have additional proofs of the justice and mercy of God, as well as of the stupidity, rebellion, and wickedness of Pharaoh and his courtiers. As these continued to contradict and resist, it was just that God should continue to inflict those punishments which their iniquities deserved. Yet in the midst of judgment he remembers mercy; and therefore Moses and Aaron are sent to inform the Egyptians that such plagues would come if they continued obstinate. Here is mercy; the cattle only are destroyed, and the people saved! Is it not evident from all these messages, and the repeated expostulations of Moses and Aaron in the name and on the authority of God, that Pharaoh was bound by no fatal necessity to continue his obstinacy; that he might have humbled himself before God, and thus prevented the disasters that fell on the land, and saved himself and his people from destruction? But he would sin, and therefore he must be punished. In the sixth plague Pharaoh had advantages which he had not before. […]

Hardened - Different words in the Hebrew. In Exo 9:34 the word means “made heavy,” i. e. obtuse, incapable of forming a right judgment; in Exo 9:35 it is stronger, and implies a stubborn resolution.