Palm Sunday started so joyfully (Luke 19:37).  Jesus was recognised as the Messiah, and the people shouted their praise.  Perhaps they thought their excitement would grow into an overwhelming affirmation of Jesus as He entered Jerusalem, and somehow, He would be accepted as King.  But Jesus saw it so differently.  As the view of Jerusalem opened up, He looked over the city; tears were in His eyes and anguish was in His heart. The city of David which should have been waiting excitedly for its King had made up its mind to kill Him, and as a consequence the city would suffer its greatest humiliation (Matthew 24:15-21).
 
Jesus, who only wanted to bring peace, would be rejected.  But His religious persecutors could not see what they were doing.  Although 'it was the Lord's will to crush Him and cause Him to suffer' (Isaiah 53:10), the hatred of His enemies would be punished.  And so, Jesus graphically predicted some of the details of the horrifying destruction of Jerusalem in AD70 by General Titus.  

Jesus also sealed His prophesy with an explanation of why it would all take place "...because you did not recognise the time of God's coming to you."  There was no shortage of information in the Scriptures about the right of Jesus to be King of kings; but most of the people in authority could not and would not see it.  So, their authority would be taken away.  By contrast, many of the ordinary people did believe in Jesus and were saved because they took Him at His Word.
 
It is the same today.  Those who are willing to accept God's Word and act on it are saved; those who refuse to do so will lose everything.  The trainee apostles would probably have found Jesus' prediction quite chilling, but also it would have spurred them later into proclaiming the Word of God and explaining the importance of responding in faith (2 Peter 3:1-13).  Hearing alone is inadequate if we do not trust what Jesus said and did on the cross - otherwise there is no defence for us on the Day of Judgement.  The gospel message is still God's powerful method of saving people.  As believers, our job is to release the gospel into a wicked world (show www.crosscheck.org.uk to your friends), encouraging those around us at home and work to recognise that Jesus has come for them and His Spirit is urging them to respond - before it is too late.