Jesus said He was going to go away, and then it would be too late for His critics to decide to follow Him.  It was a strange statement.  When He declared that He would be out of their reach, that prompted the Jews to wonder if He was contemplating suicide.  Far from it.  Jesus knew that only Father God has the right to determine when everybody enters this world and when they shall leave it.  Even though He was God, Jesus still submitted to His Father's timing and did not allow Himself to be crucified until the time that was appointed (John 12:23).
 
Jesus knew He had come from heaven and would return there (John 8:14). His religious accusers would not be able to reach Him because they did not trust Him to lead them to heaven.  Instead, they would die in their sins and face God's eternal judgement because they did not believe that He was who He claimed to be.  They thought that His claim to divinity was either a lie or blasphemy, or both.
 
This world is temporary.  Our lives are temporary.  We are not here for ever (2 Peter 3:3-7).  Everybody goes somewhere after this life (Daniel 12:2).  Jesus knew where He was going (John 16:17); He was going to return to the glory of heaven and the intimate company of Father God.  Although His accusers were very religious, they did not know where they were going.

The temporary nature of life should help us to think about where we are going when this life is finished, but if Jesus Christ is not our goal, our nervous human nature pushes such thoughts away.  We are not allowed to choose when we leave this world but it is essential that we, and those we love, desire that Jesus shall be our destination and trust Him to take us there.