Jesus was speaking the truth but they could not understand Him. They knew the meaning of the words but did not grasp the significance of the message. It was so outside their experience that they were perplexed, and sent guards to arrest Him before He stirred up the crowd because He used the words associated with the Messiah, "You will look for me". Did He mean that He would go from Jerusalem and teach Gentiles?
 
However, He was simply predicting that in a short while (the next six months) He would die, be raised from the dead and then would ascend to the Father. When that happened they would not be able to find Him. In fact nobody who resists Jesus, despises His cross and refuses to serve Him can go to heaven. They would have thrown away their opportunity.
 
Many presume that after this life they will go to a 'better place', especially if they have been religiously active. But Jesus taught that only those who submitted to Him in this life will be received into heaven. "Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven. Many will say to me on that day, 'Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles?' Then I will tell them plainly, 'I never knew you. Away from me, you evildoers!" (Matthew 7:21-23). The key to being welcomed by Jesus into His home one day is to welcome Him into our hearts now.