Have you ever prayed that if God would do something for you, then you would believe? If He would just speak to you directly, then you would be on fire for Him? "An evil and adulterous generation asks for a sign."
Why the harsh rebuke for the religious class' request? All they wanted was a sign that he was The Son of David, that he had the divine authority to speak harshly to them as he did.
But as we have seen time and again, Jesus was giving signs all over the place that He is the Messiah, the one God sent to save man. After all, how could the crowd react the way they did to Jesus' recent healing, "Is this the Son of David?" Every time he healed someone, it was a sign. Every time he performed a miracle, it was a sign. Every time he spoke with unprecedented authority from the scriptures, it was a sign. So it wasn't as though Jesus was against signs.
When we review Jesus' ministry to the point of the religious class' request, the request is foolishly arrogant. Jesus, we want you to justify to us that you have the authority to be healing and loving the people that we don't want healed or loved. They claimed to be the defenders of the true faith. They claimed to be more devout to God than all others. They created rules in order that Israel would truly be ready for when God would drive out the invaders and restore their days of glory as God's people as in the days of King David.
But, through Jesus' ministry, they are exposed as frauds. For all of their outward show that they followed God, when God is clearly moving in their midst through Jesus and His Holy Spirit, they refused to acknowledge His presence and authority. To acknowledge His approval of Jesus would mean to repent and to serve in the true kingdom of heaven as Jesus directed them. But they were not truly devoted to the living God. They were following something else that fed their need for power and adulation. They were truly an adulterous generation.
And so they refused to acknowledge the signs happening all around them. Evil people rarely call themselves evil. Instead, we find all kinds of justifications to convince ourselves and others that the evil we commit is good and/or justified. And so they publicly challenge Jesus to produce a sign just for them. He responds that he will give them the sign of Jonah.
Jonah was a reluctant prophet who was sent by God to the Assyrian capital of Nineveh to call them to repentance. Jonah refused until he was in the belly of a great fish for three days. After he was rescued from the fish, he preached repentance. In much the same way, we know now that Jesus would be in a tomb for three days. After he was raised up, his followers preached repentance and forgiveness.
He then makes some extraordinary claims that no mere teacher or prophet would make. What good prophet would claim that he is greater than Jonah? What wise teacher would claim that he is greater than Solomon? Yet, Jesus does. People who claim that Jesus was merely another teacher or prophet of God refuse to hear what this "good prophet" actually said.
How awesome would it have been to be a first-hand witness to Jesus' ministry? To see the Word that become flesh dwelling among us? What would my reaction have been to Jesus' proclamation that the kingdom of heaven is at hand? Would it have been like the disciples or the religious class?