Jesus warned His disciples of future persecution so they would not stumble and fall away from the faith when it came (John 16:1-4).  Jesus also revealed that He was going to leave them and go back to the Father (John 16:5), and this caused them sorrow (John 16:6).  Jesus explained that it was to their advantage that He leave (John 16:7), for His departure would inaugurate the future ministry of the Holy Spirit, Who will convict the world concerning sin, righteousness and judgment (John 16:8-11).  Jesus had other things to reveal to the disciples, but the coming Holy Spirit would be the One to communicate that knowledge (John 16:12-15).