Then the word of the Lord came to Jonah the second time, saying, “Arise, go to Nineveh, that great city, and call out against it the message that I tell you.” So Jonah arose and went to Nineveh, according to the word of the Lord. Now Nineveh was an exceedingly great city, three days' journey in breadth. Jonah began to go into the city, going a day's journey. And he called out, “Yet forty days, and Nineveh shall be overthrown!”The outcome Jonah had prophesied against the city of Nineveh did not occur. In the end the citizens of Nineveh repented and nothing horrible happened to their city. This displeased Jonah because he knew that some people would try to discredit the words God had told him to speak. They would claim, "We were right, nothing happened to our city just like we thought." But it's easy to confuse God relenting for God not existing, or not caring.
God used this story to demonstrate his mercy, his patience, and his steadfast love. Jonah feared that those who did not care, who smugly reassured themselves that God would do nothing, would take credit for God's mercy. However, it was not the righteousness of the doubtful that prevented God from overthrowing the city. Rather, it was the surrender of the faithful which caused God to relent. Jonah simply had to obey, what happened next was not in his hands.
I have two hearts, I really do. One for me, and one for you.