Matthew 12.38-42 and Luke 11.29-32 both relate how the "experts in the Law along with some Pharisees" (Matthew) and the "crowd" (Luke) asked Jesus for a "sign." Jesus' response is a little odd, because he points them back to the story of Jonah, and tells them their sign is the "sign of Jonah." Matthew clarifies this as being Jonah's stint in the fish's belly for three days and nights. Then Jesus continues by comparing his audience (unfavorably) with the Ninevites and the queen of Sheba. Yes, it's an odd little paragraph.
So . . . first, a little background before diving into the whole "sign of Jonah" bit: in the Synoptic Gospels (Matthew, Mark, and Luke), "signs" are bad things because every time someone wants a sign, it's because they're looking for something sensational out of Jesus. Now, it's not wrong to ask God to confirm direction he's already given you (think Gideon and the sheepskin in Judges), but in this case, Jesus considered his teaching, his healings, and his exorcisms to be plenty of proof of who he was (think John the Baptist asks who he is, and Jesus replies with fulfillment of Isaiah's restoration prophecies). Basically, these people were asking for a sign because they weren't willing to take Jesus' actions by faith. They wanted some big miracle to convince them of a truth Jesus was spending three years to demonstrate to them. So in the Synoptics, asking for a sign was, in itself, a sign of a severe lack of faith.
So Jesus gives them a sign sort of like the virgin birth sign God gave to Ahaz back in Isaiah's day: not a miracle they can point to immediately, but one that will happen in the future and will be evident to those who have faith (both the virgin birth and the resurrection were explained away by Jewish authorities, but were evident and miraculous to those who responded to the news and to Jesus in faith, as the resurrection appearances seem to have been only to his followers). In other words, Jesus responded to their confrontational lack of faith by giving them a sign that could best be understood by those with faith.
OK, so here's where it gets interesting (at least to me!). The sign of Jonah has, in my experience and reading, been limited to Matthew's explanation of the three days and nights. Fine. Works for me. But if that's the sign, what's the significance of the sign? The sign pointed to Jesus' three-day stint in the tomb, but why use that sign? Was Jesus trying to say anything else--besides pointing to his temporary death? I think he was.
Remember how Jesus then mentioned the Ninevites and the queen of Sheba? Take a look (Matthew 12):
The people of Nineveh will stand up at the judgment with this generation and condemn it, because they repented when Jonah preached to them – and now, something greater than Jonah is here! The queen of the South will rise up at the judgment with this generation and condemn it, because she came from the ends of the earth to hear the wisdom of Solomon – and now, something greater than Solomon is here!
Why mention Nineveh and the queen of Sheba? It could just be that Jesus was pointing out that even Gentiles had the faith and discernment to recognize God at work and believe, while the Jewish authorities refused to see what was right under their noses. That'd be insulting enough to these men. But it's also interesting to note that the whole story of Jonah is about God being more than just Israel's God.
Jonah is a prophet to Israel who tries to escape God's call by going to sea. That seems ridiculous to us, but in the Ancient Near East, the sea was mythically the source of chaos, destruction, and evil powers. It was the great nemesis of all the gods of all the Mesopotamian people. All of them had myths about their main gods vanquishing (or being vanquished by) sea monsters, which symbolized the power of the sea. You can see the same language in Psalms and in the prophets, but in this case, God consistently points out that he vanquishes the sea with a finger, or the "breath of his mouth." That last one's especially common, since it demonstrates so vividly how much more powerful God is than all powers on earth. But you get the point.
So why did Jonah think he could run away from God by going to sea? Well, in a lot of the early Israelite history in the Bible (especially Judges), you see a sort of tribal theology going on. In Hebrews, Japheth is praised for believing that God would protect Israel, his people, against the god and might of the neighboring tribes. In other words, Israel's god would keep Israel safe against the gods of the other peoples. So YHWH was Israel's god, just as the Hittites and Philistines had their gods. Tribal theology. What that means is that if you ticked off a tribal god, you went to another tribe, preferably one with a stronger god or one already in conflict with yours, and you could hope for some incidental protection as one god would protect his territory from encroachment by another. Crazy stuff now. But it sure seems that that's what Jonah's doing.
But look at what God does: he creates a storm (demonstrating his power over the powers of chaos), commandeers a really big fish (again, power over chaos, this time in the form of sea monsters), and spits Jonah out to preach to a bunch of heathen Gentiles. Said Gentiles repent, God is pleased, and Jonah has a royal hissy fit. Moral of the story? God is bigger than your people and your land, and his mercy and salvation extend beyond political or ethnic boundaries to include all peoples in all places. Again: God is the true God over all the earth and over all tribes, and he desires to be merciful and save all, and for all to worship him.
So put that next to Jesus' little commentary in Matthew and Luke, and suddenly it gets really interesting. What if the sign of Jonah pointed not just to the sheer stubbornness of the Jewish authorities but also to the the ramifications of Jesus' death on the cross? That God's great plan to offer salvation for all people in all places will be realized? That God is gloriously revealed as not just the God of the Israelites but as the God who created the world and has now given himself to redeem it. Pretty powerful stuff, and as a sign for those who believed in Jesus, a phenomenal paradigm shift as the mission to the Gentiles got underway.
Just a thought.