Two views of why Jesus refers the scribes and Pharisees to the sign of Jonah:
Because they are teachers of God’s Word, Jesus refers them to Scripture. What happened to Jonah proved that he was truly a prophet of the Lord who could not evade his commission. Yet Jonah’s story is also a sign of Christ, a sign that Jesus was sent by God (see Romans 1:4). Something will happen to Jesus that also happened to Jonah, and as that event had meaning for Jonah as prophet, it will have corresponding meaning for Jesus as God’s Anointed.
The generation of the scribes and Pharisees had heard from John the Baptist that the time for repentance and expectation had arrived. The winnowing fork was already in the hand of the one who would come after John, so if they did not believe in Jesus, they would be choosing the final judgment by the Lord. If they tried to excuse their unbelief by claiming that no heavenly sign legitimized Jesus, they would have failed to realize how near the judgment was. If the citizens of Nineveh had asked Jonah for proof, they would have had no time to repent, so the proof of Jonah’s preaching would have been their destruction. Those who seek more signs from Jesus insult the Judge who has come for judgment. As Nineveh was wise to repent in time, the scribes and Pharisees need to repent and believe in Jesus, to be ready for the coming of the Son of Man as judge. Those who do not listen to Jesus’ preaching on earth will see the proof they seek in his judgment, for he is more than Jonah, who was only a prophet; he is the divine Judge.
Interpretation 1:
Because they are supposed to be teachers of the Word of God, Jesus refers them to Scripture. The sign of Jonah—that which happened to him—proved that he was truly a prophet of the Lord who could not evade his commission. Yet the story of Jonah proves even more: it is also a sign of Christ, a sign that Jesus was sent by God (see Romans 1:4). Something will happen to Jesus that also happened to Jonah, and just as that event had meaning for Jonah as prophet, so it will have corresponding meaning for Jesus as God’s Anointed.1
Interpretation 2:
The generation of the scribes and Pharisees had heard from John the Baptist that the time for repentance and expectation had arrived. Judgment was imminent, and the winnowing fork was already in the hand of the one who would come after John. Therefore, if they did not believe in Jesus, they would be choosing the final judgment by the Lord Jesus. If they tried to excuse their unbelief by claiming that no heavenly sign legitimized Jesus, they would have failed to realize how near the judgment was.
If the citizens of Nineveh had asked Jonah for proof, they would have missed the opportunity to repent. The evidence of the truth of Jonah’s preaching would have been their destruction—had they refused to repent. Those who demand external signs from Jesus insult the Judge who has come for judgment. Just as Nineveh was wise to repent in time, so too the scribes and the Pharisees would have been wise to repent and believe in Jesus, to prepare themselves for the heavenly vindication of the Son of Man in the final judgment. They receive the sign they demanded as the announced sign of the final judgment. Those who refuse to listen to Jesus’ preaching on earth will experience it when heaven entrusts judgment to Jesus of Nazareth. For he is more than Jonah, who was only a prophet; indeed, he is the great divine Judge himself.2
39 But he answered them, “An evil and adulterous generation seeks for a sign, but no sign will be given to it except the sign of the prophet Jonah.