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.
We must first see what works he means, that no one may snatch at a single word, as hypocrites are wont to do; and this, as we have said, is very commonly the case under the Papacy. God had respect to their works — what works? not sackcloth, not ashes, not fasting; for Jonah does not now mention these; but he had respect to their works — because they turned from their evil way. We hence see that God was not pacified by outward rites only, by the external profession of repentance, but that he rather looked on the true and important change which had taken place in the Ninevites, for they had become renewed. These then were their works, even the fruits of repentance. And such a change of life could not have taken place, had not the Ninevites been really moved by a sense of God’s wrath. The fear of God then had preceded; and this fear could not have been without faith. We hence see that he chiefly speaks here not of external works, but of the renovation of men. 