The Pharisees and the chief priests come to Jesus. (Mark 11:27-33) They are seeking to trap Him. They ask what authority allows Him to do what He does. Jesus answered with a question. He asked them if John's baptism came from heaven or from men. They knew they couldn't say "from heaven" because Jesus would respond by asking them why they didn't believe him. They knew they couldn't say "from men" because the people considered the John a prophet. Therefore, they replied that they didn't know.
Jesus gave them the answer of His authority but they didn't get it because they were trying to please themselves without upsetting the people. (Sounds like real politicians, huh?) He essentially responded with the same question they were asking Him. They wanted to know if He was doing what He did with heaven's authority. They should have known the answer but they didn't because they were so blinded by their own selfishness.
Most people who reject Jesus as Savior believe His message came from men rather than heaven. They believe the stories are manufactured. They believe that people are misled. They believe that believers are delusional.
Saying His message is from heaven puts them in a dilemma. Then, they must ask why they haven't believed the message. Therefore, like the Pharisees and chief priests, they surround themselves with others who will support their decision that His message came from men. They give all religions the same value. They think that all of them have some value in teaching people how to live but that no one should really sell himself out to one faith. They can remain in complete control as long as they can be the judge of all faiths.
Non-believers might even think that there is plenty of time to think about these things. They might even think that they can pull the "thief on the cross" thing and believe at the very end of their lives. They don't realize that faith comes as a gift from God. They don't realize that the message that came from heaven needs a faith from heaven. They believe they can call on this at any time because they don't know that saving faith only comes from the conviction of the Holy Spirit. They don't realize that they may never think of calling on that faith in the end. They don't understand why the Bible says that "today is the day of salvation." They don't understand that they should seek the Lord "while He can be found." They don't understand that one day they will say, "No, I won't believe," for the last time.
The message of Jesus is from heaven. It requires a faith from heaven in order to believe. It is God's grace to give us that faith.
Ephesians 2:8-9 (NKJV)
For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast.