Charles Ellicott Commentary Exodus 4:21

"And Jehovah said unto Moses, When thou goest back into Egypt, see that thou do before Pharaoh all the wonders which I have put in thy hand: but I will harden his heart and he will not let the people go." — Exodus 4:21 (ASV)

All those wonders. —Not the “three signs” of Exodus 3:3-9, but the “portents” or “wonders” which were to be done before Pharaoh, and which had been alluded to in Exodus 3:20. These were, in the counsel of God, already “put into Moses’ hand,” though their exact nature was still unknown to Moses himself.

I will harden his heart. —The hardening of Pharaoh’s heart has been the subject of much controversy. It is ascribed to God in this place, and again in Exodus 7:3; Exodus 9:12; Exodus 10:1; Exodus 10:20; Exodus 10:27; Exodus 14:4; Exodus 14:8; to Pharaoh in Exodus 8:15; Exodus 8:32; and Exodus 9:34; and to the action of the heart itself in Exodus 7:13; Exodus 7:22; Exodus 9:7; Exodus 9:35.

It is conceivable that these may be simply three forms of speech, and that the actual operation was one and the same in every case. Or, three different modes of operation may be meant. It is in favor of the latter view that each term has a period during which it is predominant. In the narrative of what happened, the action of the heart itself is predominant in the first period, that of Pharaoh on his heart in the second, and that of God in the third.

We may suppose that, at first, Pharaoh’s nature was simply not impressed, and that then his heart is said to have “hardened itself,” or “remained hard;” that after a while, he began to be impressed, but by an effort of his will controlled himself and determined that he would not yield, thus “hardening his own heart;” finally, that after he had done this twice (Exodus 8:15; Exodus 8:32), God stepped in and “smote him with a spirit of blindness and infatuation,” as a judgment upon him (Exodus 9:12), thus, finally, “hardening” him .

This divine action was repeated on three subsequent occasions (Exodus 10:20; Exodus 10:27; Exodus 14:8), Pharaoh’s time of probation being past, and God using him as a mere means of showing forth His glory. There is nothing in this contrary to the general teaching of the Scriptures or to the Divine Perfection.