Jonah used this rhetorical question to show God how angry he was. Also, what Jonah said when he was back in his own country can be stated explicitly. Alternate translation: "When I was still in my own country I knew that if I warned the people of Nineveh, they would repent, and you would not destroy them" (See: [[rc://en/ta/man/translate/figs-rquestion]] and [[rc://en/ta/man/translate/figs-explicit]])
This means "you say that you will send disaster on sinners, but then you decide not to." Alternate translation: "you decide not to punish people who sin"