Jeremiah 18:8

If that nation, against whom I have pronounced, turn from their evil, I will repent of the evil that I thought to do unto them.

If that nation, against whom I have pronounced, turn from their evil. Their is emphatically in antithesis to "the evil that I thought to do."

I will repent. God herein adapts Himself to human conceptions. The change is not in God, but in the circumstances which regulate God's dealings: just as we say the land recedes from us when we sail forth, whereas it is we who recede from the land (; ). Gods unchangeable principle is to do the best that can be done under all circumstances; if, then, He did not take into account the moral change in His people (their prayers, repentance, turning from their evil way, etc.), He would not be acting according to His own unchanging principle (Jeremiah 18:9). This is applied practically to the Jews' case (; see ). So in the case of Nineveh ().