"The Sign of Jonah"
About that previous passage. Jesus (or his early followers) knew this story and associated it with "the belly of Sheol" and
whose bars closed upon me forever;
[yet Thou didst bring up my life from the Pit,]
that is, with death.
Jesus is quoted as having said ~These people are asking me for a sign, but the only sign they're going to get is "the sign of Jonah."
If this "sign" is 'spending time in death, then coming back,' it's an odd sort of evidence for Jesus to claim for his contemporary detractors. Odd, for one thing, because it arrives too late to prevent his execution, and also because it seems to be only his followers, those Jews who already love him, who see him as a resurrected person.
So I've felt for a long time that the real "sign of Jonah", to Jesus, would have been the fact that Nineveh, that most wicked of Wicked Cities, repents in this story.
For Jesus and his contemporaries, that would have symbolized the repentance of the Romans, in particular-- and of course, also those of his followers who'd been considered most sinful under the proto-Judaism of the time.
But here we have also a strong association with death, both literally and as a symbol.
Why is Jonah dead 'for three days and three nights'? Because he's been evading a divine call to give his message to the wicked foreigners: Change your ways or be destroyed. Jonah prefers to have God follow the second option; it's just what they deserve; while if they repent he knows God really will forgive them.
Look at how this resonates with the Jews of Jesus' day. Their nation has come to be politically dominated by pagans, who are systematically looting, oppressing, and corrupting their country. While their leaders are adopting Roman ways (much to the detriment of their own poor classes) there is also a widespread feeling that "God will get them for that, and serves them right." And that, people hope, will be their "return from exile," the restoration of Israel to its rightful relation with God.
And while Jesus is serving as a prophet specifically to his own people, he's been pointing out stories in which prophets found a sympathetic hearing among the wicked foreigners. And this has aroused strong hostility even in his own home village!
His nation (like any other nation!) wants to enjoy a uniquely blessed relation to God-- like Jacob before he repented and was renamed 'Israel', they want to steal their brothers' birthright and keep it for themselves. As the followers of a great many religions are tempted to do, to comfortably assume that "We've been given the straight truth, the outsiders weren't; isn't that nice!?" But there's this persistent refrain in their tradition about obligations coming with a blessed status; and they don't (like followers of any other religion) enjoy hearing that nearly as much. Friends (Quakers) come to mind in this connection.
And so this symbol of "death" also symbolizes that state, of being content to be "religious" in isolation. "Those people just wouldn't be suited to our way of worship" (as I've heard several Quakers say, in discussions of "outreach.")
The result of this kind of attitude, for any religion, is death. The religion becomes an ingrown sect, loses much of the spiritual value it used to offer its own members. (Not to all its members-- but to those content with that spiritual condition.)