Adam Clarke's Commentary on the Bible

Verse 24 (John 21:24)

This is the disciple - It is, I think, very likely that these two verses were added by some of the believers at that time, as a testimony to the truth of the preceding narration; and I allow, with Bishop Pearce and others, that it is possible that John may mean himself when he says We know, etc., yet, I think that it is very unlikely. It is certain that this Gospel loses no part of its authority in admitting the suffrage of the Church of God: it rather strengthens the important truths which are delivered in it; and in the mouths of so many witnesses the sacred matters which concern the peace and salvation of the world, are still more abundantly established. See the last note on the preceding chapter.

We know - Instead of οιδαμεν , we know, some have written οιδα μεν , I know indeed; but this is mere conjecture, and is worthy of no regard. It is likely that these verses were added by those to whom John gave his work in charge.

- Adam Clarke's Commentary on the Bible