Reference

John 15:1-17

Jesus belongs with God the Father, and He offers up His life to take our place so that we can share in His place.  Because this is who Christ is and what He's done, He is the source of life, and love, and joy.  He gives the illustration of branches that can either be separated or attached to the vine.  Without Him, all experiences of life and love and joy will be fleeting - much like the life of a branch that is removed from its vine. As His disciples are about to face terrible hardships, He encourages them to cling to Him through those things.  They are to do this for God's glory, and for their joy.