What does the historicity of the Old Testament book of Jonah have to do with Easter? Quite a bit, actually. In Matthew 12:39-41, Jesus said, An evil and adulterous generation seeks after a sign; and there shall no sign be given to it but the sign of Jonah the prophet: for as Jonah was three days and three nights in the belly of the fish; so shall the Son of man be three days and three nights in the heart of the earth. The men of Nineveh shall stand up in the judgment with this generation, and shall condemn it: for they repented at the preaching of Jonah; and behold, a greater than Jonah is here.
Jonah was a sign to the people of Nineveh in that he came back from the dead in a sense—not literally, but after having spent three days under the ocean, in the stomach of a fish. In the context of this quotation from Matthew’s Gospel, Jesus is arguing that His resurrection would prove the unbelief of the Pharisees. The people of Nineveh repented at the sign of Jonah, but the Pharisees would not repent at the greater sign of the Son of man’s resurrection from the dead. But if there never was a Jonah who spent three days and three nights in the belly of a fish, and if he never did preach in Nineveh and lead the city to repentance, the comparison would be imaginary and would prove nothing about the Pharisees. And if Jonah wasn’t literally in the belly of a fish for three days, then maybe Jesus wasn’t literally in the grave for three days, either. Jesus’ assertion that “a greater One than Jonah is here” would also be an empty claim if Jonah never actually preached at Nineveh.
There are, however, strong reasons to believe in the historicity of both the prophet Jonah and the events in the biblical book which bears his name. The strongest reason is, of course, the fact that the book of Jonah is a part of inspired Scripture, as acknowledged by both the ancient Jews and the Lord Jesus Christ. The man Jonah is mentioned in another part of the Old Testament, in 2 Kings 14:25. The historical context in which Jonah is mentioned in 2 Kings 14:25 corresponds to a period of weakness and disorder in the Neo-Assyrian Empire, during which Jonah’s warning that Nineveh would be overthrown in forty days would have been particularly believable. During this period, there was a time in which the administrative control of the Assyrian king was reduced to “greater Nineveh,” which explains why Nineveh is the main focus of Jonah’s prophecies (rather than “Assyria”). There are good reasons to believe that when Nineveh is described as a journey of three days in breadth (Jonah 3:3), with 120,000 young children (Jonah 4:11), it is the district of Nineveh that is referenced, and not just that part of Nineveh enclosed by the city wall.
Many critics have also asserted that it is impossible for a man to survive for three days and three nights in the belly of a fish. While this fish is said to have been specially prepared by God (Jonah 1:17), it still was a real fish, and it really did swallow Jonah alive. The common idea that this fish was a whale is nowhere stated in Scripture; in fact, whales are very rare in the Mediterranean, and this was more likely a great white shark, which has a much slower metabolism than a whale. It is also important to realize that the term “three days and three nights” does not necessarily refer to a full 72-hour period, but only to parts of three days. “Day and night” is a Hebrew idiom for what we would call a “day.” Among other references to “day and night” in the Bible, Jesus said that His body would be buried for three days and three nights (Matt 12:40), yet He was buried late in the day on Friday and raised at early dawn on Sunday, a period of about 36 hours.
For more detailed argumentation regarding the historicity of the book of Jonah, see my new Kindle book, The Historicity of the Book of Jonah, and Why It Still Matters.