Jonah was sent by God to the people of Nineveh to save them, but he railed against being sent to such a sinful, appalling place. Hence the trip to sea, the whale bringing him back to Nineveh. God definitely wanted him there!
So Jonah went to Nineveh, gave probably, a very reluctant and second rate sermon telling them to repent or be destroyed by the wrath of God, and left to see what God would do with them. You will have to read the whole of the book of Jonah to find out the result - the liturgists being content to leave us here with the poor tree that grows and withers, so that God can tell Jonah who is boss. It is more complicated than that of course - what in our lives might be the worm that we allow to steal in and remove Gods protection from us?