Jonah was a prophetic hero in Israel because he prophesied that Israel would have a secure Eastern border for the first time since King Solomon. When God gives him the word to go to Nineveh he knows immediately that God wants to warn them of their wickedness because of his mercy. Jonah is angry. This story is of repentance and the mercy of God. Nineveh had a repentant heart and they received mercy from God. Jonah had an unrepentant heart but God made him come face to face with His mercy in a way that Jonah didn't expect.