The early days of being with Jesus must have been very exciting for the disciples.  But now the reality of His mission (and theirs) was being spelled out.  In order to fulfil God's plan of defeating the bad works of Satan (1 John 3:8), and rescuing people who have been held in his grip (Hebrews 2:14-15), Jesus would have to sacrifice His own life (Matthew 16:21).  

Not only that, but every true disciple would have to make their lives available for anything God wanted and deny themselves what they wanted (Luke 9:23).  Discipleship should not be thought of as leisure time entertainment in pleasant company, but a commitment to spiritual warfare with all the discomforts and casualties that come with a battleground.  It was hard teaching.  Would they be prepared to identify themselves with Him or would they disown Him?  

So, Jesus challenged them that if the idea was offensive to them, and they wanted to back out (John 6:66-69), they needed to know that they would be excluded from the great victory celebration when Jesus returns in glory.  That will be a real event, not some sort of religious fiction (Matthew 24:30-31).  As a little foretaste, Peter with James and John would shortly see Jesus gloriously transfigured - an experience confirming the truth of what Jesus was saying and encouraging the disciples to stay true to Jesus all the way (Luke 9:28-36; 2 Peter 1:16-18).

Following Jesus is not just about getting God to resolve today's problems.  It is intended to be a long-term relationship in which we clearly identify ourselves with Jesus and His teaching; working with Him in God's 'family business' - as He deals with sin and its consequences and prepares His 'family' for a glorious eternal future.  Yes, short-term we will need to endure some of the 'battlefield trauma', but long-term we will also share the joys of Christ's victory and the glory of His kingdom (1 Peter 4:13).  However, those who are ashamed of the sufferings of Jesus, and who do not want to be associated with God's salvation-work, cannot share in His glory.  It was a radical choice for the disciples, and not all of them chose well: Judas was ashamed of Jesus and lost everything.  Peter was ashamed but repented and was restored. It is still a radical choice for every believer, every day at home and at work.  So, even if others ridicule your faith in Christ for a little while, do not be ashamed of Jesus, because He will honour for ever those who stand with Him now.