After Jonah got out of the whale, he went to the city of Nineveh and warned the Ninevites.
He told them that God was going to destroy them because they weren't doing what was right.
God was going to destroy them in forty days because of the evil they had done in the present and the past.
The King heeded the warning and he and everybody else covered themselves with sackcloth and began to fast.
The Ninevites turned from their evil ways after they were warned.
God saw that they had changed and he was no longer scorned.
God spared the Ninevites because they were no longer unfit.
Jehovah isn't a harsh God and that sure did prove it.