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 He did it not - God willed rather that His prophecy should seem to fail, than that repentance should fail of its fruit. But it did not indeed fail, for the condition lay expressed in the threat. “Prophecy,” says Aquinas in reference to these cases, “cannot contain anything untrue.” For “prophecy is a certain knowledge impressed on the understanding of the prophets by revelation of God, by means of certain teaching. But truth of knowledge is the same in the Teacher and the taught, because the knowledge of the learner is a likeness of the knowledge of the Teacher. And in this way, Jerome saith that ‘prophecy is a sort of sign of divine foreknowledge.’ The truth then of the prophetic knowledge and utterance must be the same as that of the divine knowledge, in which there can be no error. But although in the Divine Intellect, the two-fold knowledge (of things as they are in themselves, and as they are in their causes,) is always united, it is not always united in the prophetic revelation, because the impression made by the Agent is not always adequate to His power. Whence, sometimes, the prophetic revelation is a sort of impressed likeness of the Divine Foreknowledge, as it beholds the future contingent things in themselves, and these always take place as they are prophesied: as, “Behold, a virgin shall conceive.”