What does Jesus mean by the 'sign of Jonah'?

The 'sign of Jonah' is pivotal in understanding Jesus' prophecy of His own resurrection. He indicated that as Jonah was three days and nights in the belly of the fish, so He would be buried for three days and nights before rising from the dead (Matthew 12:40). This serves as a powerful sign of God’s grace and redemption, emphasizing the need for repentance when faced with the reality of Christ’s death and resurrection. The unwillingness of Christ's contemporaries to heed this sign underscores their spiritual blindness and shows how they rejected the profound implications of His resurrection.