In that chapter He talked to them about His love. In chapter 14 and the first part of chapter 15 Jesus gave the disciples marvelous promises that would be fulfilled because He was going away. However in chapter 15 Christ warned them that the world would try to kill them because of its hatred for Christ. Persecution is inevitable because a true disciple opposes the system of the world, which is under Satan's control. The disciples were not to be surprised that people would try to kill them in the name of religion.
History verifies that that is exactly what happened.
All kinds of atrocities take place in the name of religion. False religion always persecutes those who speak God's truth. Commitment to external religion is no guarantee that that person is a true believer. There are people who go to church, carry a Bible, and read their prayer book, yet they have no personal relationship with God. Religious people do not necessarily know God.