What is the main message of the book of Jonah?

The main message or overarching theme of the book of Jonah is God's mercy and compassion extending not just to Israel, but to all nations and peoples. Some key messages and lessons that arise from the story of Jonah include:

1. God's sovereignty and control: The story shows God's power over nature (the great fish, plant, worm) and his sovereignty in accomplishing His will, even using a reluctant prophet.
2. Obedience to God's call: Jonah's initial disobedience contrasts with his later obedience after being swallowed by the fish, teaching the importance of heeding God's voice.
3. God's mercy transcends borders: God cares about the repentance of the pagan Ninevites, demonstrating His compassion extends beyond just Israel.
4. Concern for the lost: Jonah is sent to call the Ninevites to repentance out of God's loving desire that they turn from wickedness.
5. Ethnic prejudices rebuked: Jonah's anger at God's mercy toward Nineveh exposes his nationalistic prejudices which God challenges.
6. God's grace and second chances: Despite Jonah's resistance, God persists in using him and gives him multiple opportunities.

So, while the story depicts Jonah's personal experience, the primary message points to the vastness of God's inclusive love, mercy, and redemptive purposes for all people groups, not just the nation of Israel alone.