The exhortation to endure in this life continues with the topic of the discipline of the Lord.  The Lord disciplines all His children.  Not punishes - for Christ bore the punishment for all sin, once for all.  But God does allow suffering and tribulation in our lives in order to bring about His intended result: the image of Christ being made more and more clear in our lives.  He wants us to both be filled with His joy, love and peace individually because He loves us so much, and wants us to bear the fruit of His righteousness in order to fulfill the mission of Christ to represent Him in all the world.