John 21: 20-25, Final Comments by the Eyewitness

Jesus has reappeared to the disciples several times in Jerusalem. John records one more appearance, this time later in Galilee.

John 21: 17b-19, Simon, do you love me?
Jesus said, “Feed my sheep. 
18 Very truly I tell you, when you were younger you dressed yourself and went where you wanted; but when you are old you will stretch out your hands, and someone else will dress you and lead you where you do not want to go.” 
19 Jesus said this to indicate the kind of death by which Peter would glorify God. Then he said to him, “Follow me!”

This is a strange conversation, recorded by John standing nearby. Peter, who when frightened, denied Jesus three times, is now being given instructions, with a three-times emphasis. Jesus has a plan for Peter but Peter is unsure as to what it is.

John 21: 20-23, Peter & John

Peter turned and saw that the disciple whom Jesus loved was following them. (This was the one who had leaned back against Jesus at the supper and had said, “Lord, who is going to betray you?”) 
21 When Peter saw him, he asked, “Lord, what about him?”

22 Jesus answered, “If I want him to remain alive until I return, what is that to you? You must follow me.” 
23 Because of this, the rumor spread among the believers that this disciple would not die. But Jesus did not say that he would not die; he only said, “If I want him to remain alive until I return, what is that to you?”

John responds, half a century later, to speculation that he will never die.  Not so, he assures his readers.

John 21: 24-25, John's testimony
24 This is the disciple who testifies to these things and who wrote them down. We know that his testimony is true.

25 Jesus did many other things as well. If every one of them were written down, I suppose that even the whole world would not have room for the books that would be written.

John repeats the earlier theme, from the end of the previous chapter, claiming that he was an eyewitness to all of these events and  -- added as an afterthought --  that there are many, many more things that could be written about the time Jesus spent on earth.