The one question I'm asked most often about this Gospel passage is, "What is the sign of Jonah?"
Jesus actually speaks of two signs of Jonah in the gospels, once in Matthew 12 where He explicitly assigns it to His Resurrection: "For as Jonah was three days and three nights in the belly of the whale, so the Son of Man will be three days and three nights in the heart of the earth" [Mt 12:40]
The sign seems clear: Jonah preached to the Ninevites that their city would be destroyed in 40 days. But, led by their king, the Ninevites repented, fasted and prayed, and God turned back His intent to destroy them. Here the sign of Jonah becomes a blunt “Repent or die!”
It would seem, then, that Jesus is warning His listeners to repent and believe the Good News, to put faith in His words and live. Otherwise they will suffer a great punishment.
But let's look at it from a deeper level. Nineveh was the capital of Assyria, the hated enemy of Israel, and so Jonah didn’t relish the idea of preaching to the Ninevites. If the Ninevites rejected him, they would likely kill him. But if they listened and repented, God would forgive them, they would prosper, and probably overrun Israel.
Of course, the latter is what actually happened. God strengthened Assyria, a people that didn't know Him, and used them to punish Israel for its sins. It happened just as Isaiah had prophesied: "Assyria, the rod of my anger, in whose hand is the club of my wrath! I send him against a godless nation (Israel), I dispatch him against a people who anger me" [Is 10:5-6]
Jesus is telling the Jews of His time to repent and believe in the Gospel or He will give it to the Gentiles. As He told the disciples later, Therefore I tell you that the kingdom of God will be taken away from you and given to a people who will produce its fruit. And sure enough, the punishment occurred when the Romans destroyed Jerusalem in 70 A.D.
What about us today? With so many Christians rejecting the Gospel of life and accepting what Pope John Paul II called the culture of death, we are in great need of repentance.
In Europe, the cradle of Christendom, the faith has almost disappeared from public and private life, a fact reflected in the low birth rates of nominal Christians. Could it be, we are engaged in our own self-destruction? Like the chosen people, will we be left with only a remnant of the faithful, a remnant that will be called to repent and evangelize the world to ensure God's promise to us is kept?
Is this also the sign of Jonah, a sign for today? You and I must decide.