The story of Jonah is read as the haftorah on Yom Kippur afternoon. Jonah was sent by G-d to proclaim imminent punishment to the people of Nineveh. When he took a boat in the opposite direction and a storm threatened to sink the ship, Jonah told the sailors he was the cause and told the sailors they must throw him in the sea. Jonah was saved from drowning by a whale, and after a prayer of thanksgiving to G-d, Jonah was brought to dry land.
He was asked a second time by G-d and this time went to Nineveh, warned the people, who repented sincerely and were forgiven. Jonah complained to G-d and the plant under which he had sheltered was scorched by the sun. When Jonah grieved over the loss of the plant, G-d convinced him that he was unjustified in his distress that the Ninevites had been saved.
The key lesson here is of G-d’s acceptance of repentance, even from the most wicked. Jonah’s reluctance to go to Nineveh was based on his fear that they might repent and be forgiven and that he’d be the agent of their salvation. His grudging attitude was repeatedly rebuked, and Jonah had to accept that all parts of the world are G-d’s servants, and that human life and existence are impossible without G-d’s mercy. The sudden and complete repentance of the Ninevites contrasted with the indifference with which the Israelites received prophetic announcements.
It was written in Taanit that it is not said “and G-d saw their sackcloth and ashes” , but rather “G-d saw their deeds for they repented from their evil way” (Jonah 3:10).This highlights the four aspects of repentance, acknowledging the wrong, asking for forgiveness, committing to never repeating the mistake, and changing one’s actions accordingly.
The book begins and ends with the word of G-d stressing the need for man’s acceptance of G-d’s word, and that it is impossible for a man to escape doing G-d’s will.