Jonah is one of the prohphets which is most familiar and memorable to readers. It's also a book with considerable mystery involved. Though we don't know anything about the date or author, the prophet Jonah "lived during the reign of Jeroboam II (786-746)" (p. 391). The most straightforward reading of the book would indicate that Jonah is a historical narrative. There are, however, some features which could cast doubt on the historicity.
First, there's the debate over the time in the fish. While there's argument either that it would be possible or that it would be impossible, the text clearly presents it as a miraculous event, thus leaving the argument for either point of view inadequate.
Second, there are descriptions of animals repenting and a comment on the size of Nineveh, both of which seem to be exaggerated.
There may be good reason to read the book primarily as a parable, though it is quite possible that we could also see the text as primarily an historical account, though one using a good deal of rhetorical invention.
Jonah contains a number of recurring themes and key words, including the idea of "rising up" and the idea of God "preparing" characters and events.
Some commentary on the psalm of Jonah in the belly of the fish are in order. We would possibly have expected Jonah to mourn and grieve at this time, but it does seem right to consider this as an act of God by which Jonah is preserved. He may not know what the next step is, but the animal has certainly removed him from certain death in the water.
Jonah shows that God has compassion on all sorts of people, not just the people of Israel. Jonah's lack of compassion toward those for whom God has great compassion is indicative of the way Israel did not appreciate God's desires. As we look to the New Testament we see that Jesus is the one who proclaims God's deliverance. He is the one who is greater than Jonah, who has given the sign of resurrection which he compared with Jonah's imprisonment in the fish. Jesus is greater than Jonah especially in that while Jonah worked against his own will, Jesus gave his life freely.