@peacefulpete
The message of the obvious satire is that if only Jonah had not been successful in converting Ninevah, the Assyrians would never have conquered Israel.
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The main message of the book of Jonah, however, is that the scheol, is an underwater, marine, mobile device that serves to secure living beings, including humans. The scheol allows for short-term (emergency) stay/survival (+/- 3 days) underwater, and is also capable of navigating above water and safely ascending to land. Entering with open flames or starting a fire is not possible there (unsafe exhaust and air intake, high risk of concentration of life-threatening gases).
This idea of scheol as a relatively cold place without fire is fundamentally different from the hellish ideas of the churches, but also from the JWs who associate scheol with the earth and the abstract place of all the dead. Jonah was alive there, he didn't see any other dead/living people, and there probably wasn't much room either. The JWs doctrine of the underworld would succeed if JWs considered that each dead person has a fish with a belly where the scheol is. Here, however, we must wait for new light!