Here Jesus talks of the sign of Jonah – and preceded to pick up where He left off in Nazareth… namely offending Jews by calling out their racism. They were hostile to the Gentiles and had some prophets who did not willfully accomplish the task they were given due a desire to refuse dispensing grace. Jesus in response points out the Ninevites were saved and Jonah pouts (look up Jonah 4 to compare). Jesus is giving the people a chance to be taught and changed. They choose to stay the same as they were in Jonah’s story – unwilling to do things God’s way.