Nineveh was the capital city of Israel's worst enemies in the days of Jonah. So when God called Jonah to go to Nineveh and preach a message of coming judgment if they didn't repent, the prophet ran and tried to hide from God. But God made Jonah repent of his willfulness when he was swallowed by a great fish. After three days in the belly of that fish, Jonah prayed and repented, and vowed that he would obey God.