The readings at Mass today speak about Jonah and how he was a sign to the sinful Ninevites. He was a sign that pointed out the errors of their ways. He was a sign that pointed them in the right direction--repentance.
Jesus did the same. In today's Gospel (Luke 11: 29-32), He called the people crowding around Him "an evil generation." They were headed in the wrong direction, looking for wondrous signs rather than what the signs were pointing toward--a conversion of heart that would lead to knowing and following Jesus. So Jesus called them to repent the way the Ninevites had done.
I can't help thinking, though, about how different Jonah and Jesus were. Jonah ran from preaching to the Ninevites. At first we might think it was because he was afraid that they would string him up for his challenging message, but the truth is told in the last chapter of the Book of the Prophet Jonah where he is angry and complains: "This is why I fled at first to Tarshish. I knew that you are a gracious and merciful God, slow to anger, rich in clemency, loathe to punish." Jonah did not want the Ninevites--a foreign people and his enemies--to have any opportunity to hear the call to repent because he knew if they did repent, God would forgive. He wanted them to be destroyed by their sins.
It's clear that while Jonah was pointing out to the Ninevites, with one finger as it were, their need for repentance, he had three fingers pointing back at himself, unaware of his own need for repentance. Jonah was called to speak the truth--that the Ninevites were engaged in evil and needed to repent--with love, hoping and praying for their repentance so that God could shower His mercy upon them.
Jesus is a sign to people of all time. According to the Gospel of Mark, when Jesus began his public ministry He said: "This is the time of fulfillment. The kingdom of God is at hand. Repent, and believe in the gospel" (1: 15). Like Jonah, He calls for repentance, but unlike Jonah, He longs for people to admit their sins, ask for God's mercy, and then receive it.