Why did Jesus say "you will be put to death" and yet "not a hair of your head will perish"? Jesus' words here contain an apparent contradiction:


  You will be betrayed even by parents, brothers, relatives and friends, and they will put some of you to death. All men will hate you because of me.  But not a hair of your head will perish. By standing firm you will gain life.


Luke 21:16-19

How can someone be "put to death" and yet "not a hair of their head will perish"?
Jesus is talking here about the resurrection of the dead. Because of what Christ did all will live again. So yes you could die for the gospel but you would gain eternal life in Christ. 

Just adding some scripture to back this up:


  (KJV) 1 Corinthians 15:42 So also is the resurrection of the dead. It is sown in corruption; it is raised in incorruption:


Just supporting that we will be raised from this mortal state which is corruptible (hence why we die) to an immortal state that is incorruptible.