If Jesus rose from His tomb Sunday morning after being interred Friday evening, we have no Savior! Jesus gave only one sign of His Messiahship: "...so will the Son of Man be three days and three nights in the heart of the earth."
Why did the Pharisees ask Him for a sign? The answer appears in the section immediately preceding their request. Jesus had been preaching that "a tree is known by its fruit" (verse 33), so naturally, these Jews asked for a sign from Jesus to prove He was the Messiah! They wanted to see what fruit He would produce!
Jesus swiftly rebuked them because they had completely missed the point (verses 41-42). To satisfy their curiosity, they wanted to see a miracle, but the fruit Jesus meant was repentance, good works, and spiritual growth. He would make them wait to see the fruits of His ministry.
Thus He says, paraphrasing, "The only sign that will absolutely prove the truth of My message is one that I will have no control over. I will be exactly three days and three nights in the grave. I will be dead. I will not be able to resurrect Myself. So if God the Father resurrects Me after exactly three days and three nights, it will be proved beyond doubt that I am the Messiah."
He gave the same sign in other places to different audiences, each time using similar wording. In John 2:19-21, He says, "'Destroy this temple, and in three days I will raise it up.' . . . But He was speaking of the temple of His body."
To His disciples, He says, "The Son of Man is being delivered into the hands of men, and they will kill Him. And after He is killed, He will rise the third day" (Mark 9:31; 10:33-34; Matthew 17:22-23; 20:18-19; Luke 9:22).