God saw their works, that they turned from their evil way. God repented of the evil which he said he would do to them, and he didn't do it.
And in the very place, where Scripture saith, “He repenteth,” it is said a little after, “He is not a man that He should repent.” When then He changes His works through His unchangeable counsels, He is said to repent, on account of the change, not of the counsel, but of the act.” Augustine thinks that God, by using this language of Himself, which all would feel to be inadequate to His Majesty, meant to teach us that all language is inadequate to His Excellences. “We say these things of God, because we do not find anything better to say. I say, ‘God is just,’ because in man’s words I find nothing’ better, for He is beyond justice. It is said in Scripture, “God is just and loveth justice.” But in Scripture it is said, that “God repenteth,” ‘God is ignorant.’ Who would not start back at this? Yet to that end Scripture condescendeth healthfully to those words from which thou shrinkest, that thou shouldest not think that what thou deemest great is said worthily of Him. If thou ask, ‘what then is said worthily of God? one may perhaps answer, that ‘He is just.’ Another more gifted would say, that this word too is surpassed by His Excellence, and that this too is said, not worthily of Him, although suitably according to man’s capacity: so that, when he would prove out of Scripture that it is written, “God is just,” he may be answered rightly, that the same Scriptures say that “God repenteth;” so, that, as he does not take that in its ordinary meaning, as men are accustomed to repent, so also when He is said to be just, this does not correspond to His supereminence, although Scripture said this also well, that, through these words such as they are, we may be brought to that which is unutterable.” “Why predictest Thou,” asks Chrysostom, “the terrible things which Thou art about to do? That I may not do what I predict. Wherefore also He threatened hell, that He may not bring to hell. Let words terrify you that ye may be freed from the auguish of deeds.” “Men threaten punishment and inflict it. Not so God; but contrariwise, He both predicts and delays, and terrifies with words, and leaves nothing undone, that He may not bring what He threatens. So He did with the Ninevites. He bends His bow, and brandishes His sword, and prepares His spear, and inflicts not the blow. Were not the prophet’s words bow and spear and sharp sword, when he said, “yet forty days and Nineveh shall be destroyed?” But He discharged not the shaft, for it was prepared, not to be shot, but to be laid up.”