John was the last of the original disciples.  He'd seen everyone he knew and loved die around him, and as he sat alone in exile, he probably had many questions about his life.  Jesus, though, showed him that his usefulness was never ending...that he still had a purpose, a chance to do good.  He showed him what is to come, not to scare him or lead him to scare others, but to assure him that love is at the center, and as long as there is life, there is hope.