Jn 21:20-25
20Peter turned and saw the disciple following whom Jesus loved, the one who had also reclined upon his chest during the supper and had said, “Master, who is the one who will betray you?” 21When Peter saw him, he said to Jesus, “Lord, what about him?” 22Jesus said to him, “What if I want him to remain until I come? What concern is it of yours? You follow me.” 23So the word spread among the brothers that that disciple would not die. But Jesus had not told him that he would not die, just “What if I want him to remain until I come? [What concern is it of yours?]”
24It is this disciple who testifies to these things and has written them, and we know that his testimony is true. 25There are also many other things that Jesus did, but if these were to be described individually, I do not think the whole world would contain the books that would be written.
THE WORD SPREAD AMONG THE BROTHERS: Scholars believe that the Fourth Gospel possibly ended with chapter 20. The supplementary chapter 21 probably came from another collection of the post-resurrection appearances of Jesus and was added by the final redactor to the work of the evangelist. The story represents a Galilean tradition of the appearance of Jesus and involves three characters: the Seven (disciples) as a group, and then Simon Peter and the Beloved Disciple individually.
The ever-rash Peter (even after his moving reconciliation with Jesus) questions Jesus about the fate of the Beloved Disciple, and Jesus replies with an enigmatic saying, “What if I want him to remain until I come?” It could have been not much more than a “None of your business” reply to Simon, but in the Johannine community, it was misunderstood by some as a prediction that the Disciple would still be living until the second coming of Jesus (in the early Church, there was widespread belief in the imminence of the parousia). With the death of the Beloved Disciple, the faith of some Johannine Christians would have been shaken. This incident is narrated to clarify the difficulty and strengthen the Christians after the demise of their hero.