Remember the word that I said unto you, The servant is not greater than his lord. If they have persecuted me, they will also persecute you; if they have kept my saying, they will keep yours also.
Note 69 at Joh 15:20: Pr 13:12 says, "Hope deferred maketh the heart sick." If believers have the mistaken opinion that they will not suffer persecution, then their hearts will be sick quite often. Jesus was preparing His disciples for the inevitable so that they would not be offended when it came (Joh 16:1-4).
Note 70 at Joh 15:20: In the midst of persecution, Satan will try to convince us that this strife is all our fault. If he succeeds, then we back down, and the pressure is off his followers. However, Jesus suffered continual rejection and persecution, yet we know that the problem was not with Him but with those who rejected Him.
Jesus was making it clear that persecution is an inevitable part of a godly life (2Ti 3:12) so that we will not fall prey to introspection and self-condemnation when rejection comes. If our sinless Savior was rejected, then certainly we will be too.