The religious leaders of Jesus’ time requested a sign of Him to prove His authority saying,
These leaders were not sincere in their request for they have not regarded all the mighty works that Jesus had already done. Each proof of divinity made them more determined to stop His work until finally after Jesus resurrected Lazarus from the dead, they planned to not just silence Jesus but to kill Him.
The religious leaders had no right to demand a sign because they had closed their eyes to the fulfillment of the Old Testament prophecies concerning the Messiah. In “Moses and the prophets” (Luke 16:31) there was enough evidence to help them see the truth. But their ambition for worldly gain and power made them refuse the spiritual kingdom of God that Jesus preached and testified of in the OT Scriptures (John 5:45–47). If Jesus responded to their insincere demands, He would be casting “pearls before swine” (Matthew 7:6).
So, Christ instead gave them the sign of Jonah saying,
“An evil and adulterous generation seeks after a sign, and no sign will be given to it except the sign of the prophet Jonah. 40 For as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth” (Matthew 12:39-40).
How was the prophet Jonah a “sign”? Jonah’s ministry was a sign in two ways:
First: Jonah spent 3 days in the belly of the whale. In like manner, Christ spent in 3 days in Joseph’s tomb, from late Friday afternoon to early Sunday morning. Christ’s resurrection was the ultimate miracle of His ministry on earth.
Second: The Ninevites “repented” although Jonah performed no miracles for them. They accepted his message because they were convinced for their guilt (Jonah 3:5–10). In contrast, the religious leaders should have accepted the words of truth the Christ shared with them. And they should have repented of their sins (Mark 1:22, 27). And in addition to Christ’s words, He also performed many mighty miracles that bore divine evidence to the truthful of His words (John 5:36). Yet, in spite of all these clear proofs, the religious leader rejected Christ and chose to disobey the pleadings of the Holy Spirit.
In His service.