Because Jesus speaks of it,
And Jesus was God's Son,
Incapable of any kind of error.
If he was wrong about Jonah,
He could have been wrong about everything else,
So he wasn't,
That's the way the argument goes among many apologists who assume the Bible has to be without error - inerrant. Thom Stark begs to differ, but unlike most of us isn't content to just harrumph and move on without tackling the logic head on.
Jesus never taught that David wrote Psalm 110, or that Daniel wrote the book of Daniel, or that the book of Jonah is historically accurate. At the very most, he assumed these things. But not even this is guaranteed. (p.53)
According to the logic of fundamentalism, if Jesus assumed traditions that were wrong, then Jesus himself would have been wrong - and the whole religion (apparently) collapses in on itself. (p.54)
This is also the logic of the more simple-minded atheistic rejections of Christianity, and fundamentalists have no one but themselves to blame for setting up such a stupid argument in the first place. Stark however is no atheist. His response is that Jesus must have learned like the rest of us as a child, correcting faulty assumptions as he grew, so "why can we not grant that there were still some lingering faulty assumptions into his adulthood?" To think otherwise is to get netted in the heresy of docetism, which denies Jesus' humanity.
If Jesus believed the world was flat, and that Daniel wrote Daniel, it is not because he was an inferior or imperfect being; it's because he was fully a human being.
Just because Jesus is portrayed in the gospels as assuming a first century worldview doesn't mean we need to. No need to sweat the tale of the big-bellied fish, shonky predictions made after the fact in the book of Daniel, or the belief that demons caused epilepsy for that matter.
Works for me.
To be continued.