What does John 21:25 mean?

Throughout the gospel of John, there have been overtly anonymous references to a particular disciple (John 1:37; 13:23; 18:15–16; 19:26; 21:23). The prior verse seems to confirm this person is John, the author of the entire work (John 21:24). John may have used a secretary to write down his words as he spoke, partly explaining why this writing ends with a specific claim to authorship. There appears to be an additional stamp of approval, possibly from a local church, attached to that statement as well.

Here, the "signature" concludes with the gospel of John's only explicit use of a first-person perspective. It's not entirely clear if this is still John speaking, or if this continues the note of approval which began with the phrase "and we know…" from the prior verse. Either way, it makes the point that Jesus' earthly ministry could not be fully detailed in a single book. Further, to explain or understand those words would require immense effort. The existence of Bible commentaries—such as this very ministry—which are many times longer than the text itself is further proof of this.

The Truth John proclaimed as the very "Word of God" (John 1:1) defies our attempts at perfect explanation (Isaiah 55:8–9; 2 Peter 3:16; Hebrews 5:11). That which God has included in Scripture is not enough to answer every possible question we may ever have. Yet it more than adequately tells us what we must know to be restored with God (John 20:30–31).