2) The book of Jonah announces the coming of Jesus Christ – Jonah is a foreshadowing of Jesus' coming. The Lord himself tells us this very clearly in the Gospel.
When asked by the Jews to give them a sign that would openly reveal him as the Messiah, he replied, according to Matthew: "No sign will be given to this generation except the sign of the prophet Jonah. For just as Jonah was three days and three nights in the belly of the whale, so will the Son of Man be three days and three nights in the heart of the earth" (Mt 12:39f).
Luke's version of Jesus' words is simpler: "This generation [...] seeks a sign, but no sign will be given to it except the sign of Jonah. For as Jonah was a sign to the people of Nineveh, so will the Son of Man be to this generation" (Lk 11:29f). We see two elements in both texts: the Son of Man himself, Christ, the one sent by God, is the sign. The Paschal Mystery points to Jesus as the Son of Man; he is the sign in and through the Paschal Mystery.
In the Old Testament account, this mystery of Jesus shines through very clearly.
In the first chapter of the book of Jonah, there is mention of a threefold descent of the prophet: he descends to the port of Joppa; he descends into the ship; and in the ship he puts himself in the most hidden place. In his case, however, this threefold descent is an attempted escape from God. Jesus is the one who descends out of love, not to flee, but to reach the Nineveh of the world: he descends from his divinity into the poverty of the flesh, of being a creature with all its miseries and sufferings; he descends into the simplicity of the carpenter's son, and he descends into the night of the cross, and finally even into the night of Sheol, the world of the dead. In doing so, he goes before us on the path of descent, far from our false glory as kings; the path of penance, which is the path to our own truth: the path of conversion, the path that leads us away from Adam's pride, from wanting to be God, towards the humility of Jesus who is God and who strips himself of his glory for us (Phil 2:1-10). Like Jonah, Jesus sleeps in the boat while the storm rages. In a certain sense, in the experience of the cross, he allows himself to be thrown into the sea and thus calms the storm. The rabbis interpreted Jonah's words, "Throw me into the sea," as the prophet's offering of himself in order to save Israel: he was afraid of the conversion of the pagans and Israel's rejection of the faith, and for this reason, they say, he wanted to be thrown into the sea. The prophet saves by putting himself in the place of others. Sacrifice saves. This rabbinical exegesis became truth in Jesus.
[Pope Benedict XVI, Cardinal Ratzinger, Lectio in s. Maria in Traspontina, 24 January 2003; in "30Giorni" February 2003]