Sign of Jonah: Everyone is part of a generation. One inherits not only the blessings and divine promises granted one’s ancestors but also the sin of preceding generations (Mt 23:35-36). Generation or genealogy, therefore, refers to the solidarity of the descendants of one family or race. The Jewish people emphasize their solidarity, in blessing or in sin, from Adam to Abraham and Moses—or to Christ as in the case of early Christians—and even to the end of time.
Matthew speaks of the sign of Jonah in terms of Jesus’ resurrection—three days in the whale’s belly, three days in the earth (Mt 12:39-40). For Luke, the sign of Jonah refers to the fact that the people of Nineveh, the capital of the Assyrian Empire in eighth century BC, repent upon hearing the prophet’s warning (v 32).
Jesus comes in fulfillment of the promise made by Yahweh to his people. He is greater than Solomon or Jonah whose preaching the Ninevites heeded. He is the sign for the present generation. By refusing to believe Jesus, this later generation of Ninevites forfeit the blessings their forefathers gained.