And the heart of Pharaoh was hardened, neither would he let the children of Israel go; as the LORD had spoken by Moses.

And his heart was hardened, and the heart of his servants, and it was made exceeding hard: neither did he let the children of Israel go, as the Lord had commanded by the hand of Moses.

And the heart of Pharaoh was stubborn, neither would he let the children of Israel go, as Jehovah had spoken by Moses.

and the heart of Pharaoh is strong, and he hath not sent the sons of Israel away, as Jehovah hath spoken by the hand of Moses.

And the heart of Pharaoh was hard, and he did not let the people go, as the Lord had said by the mouth of Moses.

And his heart was weighed down, along with that of his servants, and it was hardened exceedingly. Neither did he release the sons of Israel, just as the Lord had instructed by the hand of Moses.

Et obduruit cor Pharaonis, nec dimisit filios Israel, sicut loquutus fuerat Jehova per manum Mosis.

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

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. The magicians, by their successful imitations of the miracles wrought by Moses, made it doubtful to the Egyptians whether Moses himself was not a magician acting without any Divine authority; but the plague of the boils, which they could not imitate, by which they were themselves afflicted, and which they confessed to be the finger of God, decided the business.
Pharaoh had no longer any excuse, and must know that he had now to contend, not with Moses and Aaron, mortals like himself, but with the living God. How strange, then, that he should continue to resist! Many affect to be astonished at this, and think it must be attributed only to a sovereign controlling influence of God, which rendered it impossible for him to repent or take warning. But the whole conduct of God shows the improbability of this opinion: and is not the conduct of Pharaoh and his courtiers copied and reacted by thousands who are never suspected to be under any such necessitating decree? Every sinner under heaven, who has the Bible in his hand, is acting the same part. God says to the swearer and the profane, Thou shalt not take the name of the Lord thy God in vain; and yet common swearing and profaneness are most scandalously common among multitudes who bear the Christian name, and who presume on the mercy of God to get at last to the kingdom of heaven! He says also, Remember the Sabbath day to keep it holy; thou shalt not kill; thou shalt not commit adultery; thou shalt not steal; thou shalt not bear false witness; thou shalt not covet; and sanctions all these commandments with the most awful penalties: and yet, with all these things before them, and the professed belief that they came from God, Sabbath-breakers, men-slayers, adulterers, fornicators, thieves, dishonest men, false witnesses, liars, slanderers, backbiters, covetous men, lovers of the world more than lovers of God, are found by hundreds and thousands! What were the crimes of the poor half-blind Egyptian king when compared with these! He sinned against a comparatively unknown God; these sin against the God of their fathers - against the God and Father of Him whom they call their Lord and Savior, Jesus Christ! They sin with the Bible in their hand, and a conviction of its Divine authority in their hearts. They sin against light and knowledge; against the checks of their consciences, the reproofs of their friends, the admonitions of the messengers of God; against Moses and Aaron in the law; against the testimony of all the prophets; against the evangelists, the apostles, the Maker of heaven and earth, the Judge of all men, and the Savior of the world! What were Pharaoh's crimes to the crimes of these? On comparison, his atom of moral turpitude is lost in their world of iniquity. And yet who supposes these to be under any necessitating decree to sin on, and go to perdition? Nor are they; nor was Pharaoh. In all things God has proved both his justice and mercy to be clear in this point. Pharaoh, through a principle of covetousness, refused to dismiss the Israelites, whose services he found profitable to the state: these are absorbed in the love of the world, the love of pleasure, and the love of gain; nor will they let one lust go, even in the presence of the thunders of Sinai, or in sight of the agony, bloody sweat, crucifixion, and death of Jesus Christ! Alas! how many are in the habit of considering Pharaoh the worst of human beings, inevitably cut off from the possibility of being saved because of his iniquities, who outdo him so far in the viciousness of their lives, that Pharaoh, hardening his heart against ten plagues, appears a saint when compared with those who are hardening their hearts against ten millions of mercies. Reader, art thou of this number? Proceed no farther! God's judgments linger not. Desperate as thy state is, thou mayest return; and thou, even thou, find mercy through the blood of the Lamb.
See the observations at the conclusion of the next chapter. See Clarke at Exodus 10:29 (note).

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, Exodus 4:21.