John 21:24

This is the disciple which testifieth of these things
Recorded in this chapter concerning the appearance of Christ to his disciples at the sea of Tiberias, and what were done by him in their presence, what passed between them; particularly the conversation he had with Peter, both concerning himself, and the disciple John: and also, of all things that are written in this whole Gospel. These are testified to be true by this very disciple John, concerning whom the above report went upon a mistaken sense of Christ's words, and who himself

wrote these things;
all that is contained in this book, as well as the particulars relating to this conversation of Christ with Peter:

and we know that his testimony is true.
The testimony of one that was an eye and ear-witness, as John was, of all that he testified and wrote, must be known, owned, and allowed by all to be true, firm, and unquestionable; and therefore the apostle speaks in the plural number, as being not only his own sense, but the sense of all men. Though some take this to be the attestation of the Ephesian church, or of the bishops of the Asiatic churches, who put John upon writing this Gospel; of which they give their judgment and testimony, as believing it to be a true and faithful narrative.