How do we know that Christ is the central sign of God?

The sign of the prophet Jonah, mentioned by Jesus in Matthew 12:38-41, points directly to the work of Christ—His death, burial, and resurrection. Just as Jonah was three days in the whale's belly, Christ would be three days in the heart of the earth. This teaching encapsulates the essence of the gospel: Christ crucified and rising again is the definitive sign of God's redemptive plan. All of Scripture ultimately testifies of Christ, highlighting that He is the one sign we cannot miss if we seek eternal life (John 5:39).