"Just as Jonah was three days and three nights in the fish, so Jesus will be three days and nights in the earth." Jesus is the one to point this out to his audience. Jesus would be three days and three nights in the earth. But then he would be raised from the dead. Then, he would reveal himself in glory. The figuratively resurrected Jonah was a "sign" to the people, and they repented. The wicked people of Nineveh repented at the preaching of Jonah, but the rebellious people of Jerusalem would not repent at the preaching of Jesus. You and I look to the resurrected Jesus, and we believe his testimony; we believe the "signs" and repent and turn to God. Jonah, in this way, foreshadows our savior.