Vonnegut draws parallels to the biblical Book of Jonah in Cat's Cradle as a way of supporting themes about the incomprehensibility of God's plan and the inability of man to resist destiny. In the Bible, Jonah lives near the city of Nazareth. God commands him to travel to another city named Nineveh to prophesy to the people their impending destruction if they do not change their sinful ways. Jonah, however, angrily resists. He attempts to flee to Tarshish on a ship, but God sends a storm to interrupt the voyage. The other shipmen are frightened and entreat their gods to save them in light of this disaster. They find Jonah asleep in the sides of the ship, and the shipmaster asks him to also pray to his god for salvation. Soon the shipmen discover that Jonah is the reason for their danger, and they decide to throw Jonah into the ocean at his suggestion. Jonah is then swallowed by an ocean creature, usually interpreted as a whale, and he survives in its belly for three days. He prays to God for his release, and Jonah is vomited from the mouth of the whale.
When he is released from the whale, again the Lord directs him to Nineveh. Jonah obeys and prophesies their destruction in forty days if they do not repent, so the people fast and wear sackcloth to show their penitence. Jonah, still an angry fellow, is unhappy at the idea of God saving the people of Nineveh, so he leaves the city and sits upon a hill to see whether God will destroy it or not. While he is sitting there, God causes a gourd to grow above his head so that he might have shade. Jonah is glad for this gourd, but God then causes a worm to kill the gourd and the sun beats upon Jonah's head (creating the joke that things are now too hot for the hot-headed man). Jonah wishes for death, because he believes it better for him to be dead than alive, and he is very angry that the gourd died. God confronts Jonah and asks why he values the gourd more than the people of Nineveh, since the people of Nineveh cannot distinguish between their right hand and their left hand.
The Book of Jonah has been important in theologians' interpretation of the ideas of destiny and God's will. Jonah is intent on defying God and following his own desires, but he is unable to resist God's divine plan. God used Jonah as he saw fit, and he remained unchanged by Jonah's desire to be uninvolved in the salvation of Nineveh. Further, it is important to note that although the people of Nineveh are sinful, they are given the opportunity to repent and gain salvation through the grace of God. Because the people of Nineveh were ignorant of their sin, God proclaimed them worthy of mercy as long as they chose to repent for their transgressions.
Most scholars believe the story of Jonah is fictitious because the idea of being swallowed by a whale seems so fantastic. Yet, there have been documented cases of humans being subject to similar plights, such as the seaman who was swallowed by a sperm whale in the 1900s near the Falkland Islands. Although he had damage to his skin and was unconscious when he was recovered, he managed to survive being inside the whale for three days.
Jonah is often interpreted as a figure for Christ, a view that was first proposed by Augustine. As Jesus would be, Jonah was taken from the world for three days and returned after that period with a message of salvation for the people.
