This death only - Pliny calls locusts a pestilence brought on by divine wrath. Pharaoh now recognizes the justice of his servants' apprehensions, Exodus 10:7.

Forgive, I pray thee, my sin only this once - What a strange case! And what a series of softening and hardening, of sinning and repenting! Had he not now another opportunity of returning to God? But the love of gain, and the gratification of his own self-will and obstinacy, finally prevailed.

Now therefore forgive, I pray thee, my sin, only this once,.... Pretending that he would never offend any more, and if he did, he did not desire it should be forgiven him, but that due punishment should be inflicted on him. These words are directed to Moses, he being the principal person that came to him with a commission from the Lord, and who was made a god to Pharaoh; and therefore he does not ask forgiveness of the Lord, but of Moses:

and entreat the Lord your God, that he may take away from me this death only; this deadly plague of the locusts, which devouring all the fruits of the earth, must in course produce a famine, and that the death of men. Moreover, the author of the book of Wisdom says, that the bites of the locusts killed men,"For them the bitings of grasshoppers and flies killed, neither was there found any remedy for their life: for they were worthy to be punished by such.'' (Wisdom 16:9)Pharaoh was sensible that this plague came from God, and that he only could remove it; and therefore begs the prayers of Moses and Aaron to him for the removal of it, and suggests that he would never desire such another favour; but that if he offended again, and another plague was inflicted on him, he could not desire it to be taken away; by which he would be understood, that he determined to offend no more, or give them any occasion for any other judgment to come upon him, was he once clear of this.

Now therefore forgive, I pray thee, my sin only this once, and entreat the LORD your God, that he may take away from me this death only.

10:17 Pharaoh desires their prayers that this death only might be taken away, not this sin: he deprecates the plague of locusts, not the plague of a hard heart.

10:12-20 God bids Moses stretch out his hand; locusts came at the call. An army might more easily have been resisted than this host of insects. Who then is able to stand before the great God? They covered the face of the earth, and ate up the fruit of it. Herbs grow for the service of man; yet when God pleases, insects shall plunder him, and eat the bread out of his mouth. Let our labour be, not for the habitation and meat thus exposed, but for those which endure to eternal life. Pharaoh employs Moses and Aaron to pray for him. There are those, who, in distress, seek the help of other people's prayers, but have no mind to pray for themselves. They show thereby that they have no true love to God, nor any delight in communion with him. Pharaoh desires only that this death might be taken away, not this sin. He wishes to get rid of the plague of locusts, not the plague of a hard heart, which was more dangerous. An east wind brought the locusts, a west wind carries them off. Whatever point the wind is in, it is fulfilling God's word, and turns by his counsel. The wind bloweth where it listeth, as to us; but not so as it respects God. It was also an argument for their repentance; for by this it appeared that God is ready to forgive, and swift to show mercy. If he does this upon the outward tokens of humiliation, what will he do if we are sincere! Oh that this goodness of God might lead us to repentance! Pharaoh returned to his resolution again, not to let the people go. Those who have often baffled their convictions, are justly given up to the lusts of their hearts.