In the teachings of Jesus in the gospel of John: If you are free to sin (to lie, hate, commit adultery, etc) you are not free. If you are free to sin you are a slave to sin. If you cannot sin you are truly free. John expressed this further in his epistles. Because of the importance of the veracity of John's testimony of Jesus' teachings like this one the later disciples had to focus on who learned from John so a disciple of John came to the fore named Polycarp. Yet today we have a witness alive still namely Lord Jesus Himself and by following the teachings in John's writing we can actually find that Jesus confirms these His teachings directly to each follower by keeping the promises to disciples of His interspersed within those teachings. He is alive to do this and His word is in Revelation - the book John wrote based on Jesus' appearance to Him long after Jesus rose from the dead - that He, Jesus Christ, is the one who lives and was dead and is alive forever - even holding the keys of death and the place of the dead.
