A do-over.
Chapter 3 starts off in much the same way as chapter 1: "The word of the Lord came to Jonah." It's almost like God says, okay, let's try this again, a second chance to get it right.
I am so grateful for second chances! Even in teaching, I find I improve so much the second time I teach a lesson or a course. I can reflect on what went right and and adjust what was not as effective as it should have been. God gives us all second (and third and fourth) chances to make things right with Him and with each other. We need to embrace the second chances to restore relationships!
Jonah's second chance was qualified. The first time God told him to preach in Nineveh because of their evil. This time God told Jonah to speak the words God would tell him. This is the thing about God: He knows our hearts and attitudes and we can't fake authentic obedience. We can go through the motions, and God will use us to do His work, but there's a difference between obeying God because we love Him and going through the motions of obedience (more on that later). Jonah did go to Nineveh and he told the people they had 40 days before their city would be destroyed. I find it curious that there wasn't a specific call to repent and turn to God. It makes me think that the people were trying to find a path to satisfaction or happiness in the ways they understood: pleasure, education, and gods they could see. When Jonah pointed out the end result of human effort, he didn't have to say "repent" because they recognized the futility of their actions.
When the king called on people to repent, even he wasn't sure that their turning from evil would save them, but he hoped that God would relent and let them live. And God relented, a second do-over.
God is patient and merciful. He will give people second chances to follow Him, no matter who they are or what they've done (1 John 1:9).