John 21:23-25 -We know that his testimony is true

21:23

John knew that people would assume that Jesus’ words meant that John would not die, but would see the return of Jesus. By the way, this is also evidence that the beloved disciple, and the one who wrote the gospel, is indeed John the Apostle. John here stresses that Jesus did not actually say that John would not die, rather He was stressing that Peter did not need to concern himself with what Jesus’ plans for John were.

21:24,25

John now makes it even clearer that it is he, the apostle John, who is writing this gospel. I suppose it is actually possible that these last two verses were written by someone else, and that this person is making it clear here that all the preceding material comes from John the Apostle. The gospel finishes with an acknowledgement that the gospel contains only a small selection of the things that Jesus did. Jesus did many more things. Some of them are recorded in the synoptic gospels, but He did even more things than those.