Jonah

Basically, the people of Nineveh were Jonah’s enemies, or at least certainly not his friends.

So when God told Jonah to go and tell them to repent of their sins, Jonah did not want to do it. He did not want them to be saved. Like a rebellious child, he protested and went the other way, boarding a ship instead.
God blocked his way, much as a parent stops a child from going where he has been told not to go. As a result, Jonah was thrown overboard and swallowed by a great fish, shown at the top left of the painting.
Jonah remained there for three days, and during that time he prayed, shown at the top right, before being deposited upon the shore.

After this, Jonah did what he had been told to do and went to preach in Nineveh, shown at the bottom left. Just as he had expected, when the people heard about their sin and about Jonah’s God, they repented.
Jonah then went outside the city to pout, because he told God that this was exactly what would happen, and he did not like it. He sat under a plant that sprang up to give him shade, but God sent a worm to destroy the plant.

Jonah felt sorry for the plant, and God used that to teach him a lesson. If Jonah could care so much about a plant that he had not made grow, then should not God care even more for the people of Nineveh?
God said to Jonah: “You had compassion on the plant for which you did not work and which you did not cause to grow, which came up overnight and perished overnight. And should I not have compassion on Nineveh, the great city in which there are more than 120,000 persons who do not know the difference between their right and left hand, as well as many animals?”

The message of Jonah is that God has compassion on people, and He forgives those who repent.