John's Gospel ends in a very intriguing way. He declares himself to be the Apostle John (through a very eloquent transition from a narrative concerning himself) and signs off by saying, "Now there are also many other things that Jesus did. Were every one of them to be written, I suppose that the world itself could not contain the books that would be written." That's an interesting thing to say.
He said something not too long before this point in 20:30-31 where he interrupts the narrative in order to declare his purpose for writing. That is, he wrote his Gospel so that his readers might have life through faith in Jesus who is the Christ and Son of God. There were many signs that Jesus performed and yet, it seems, John chose to record particular ones to accomplish his literary purpose. Yet this one in chapter 21 goes a step further. Not only did he choose to record certain things but if you were to record all the things that Jesus did that you'd run out of room in the world to record it.
This seems weird at first for a couple of reasons. First, it's obvious to anyone reading that Jesus did many other things. There's no birth narrative, no Sermon on the Mount, etc. Even without the Synoptic Gospels (Matthew, Mark, and Luke) we can reason that Jesus' life involved a lot more than what John is giving us. And so, in that sense, John's statement doesn't need to be said.
And so, we may ask, what does John mean by all Jesus did? How specific should our minds go here? He likely is not stating the obvious that Jesus did a whole host of things: eat, sleep, bathe, and those many times over. Rather, it seems no stretch of the imagination that John is communicating that there are many other things that Jesus did that one might want to include in a gospel and yet, with his 20:31 purpose statement in view, he recorded what he did so that we might believe in this Jesus.
The second puzzling factor is the comment about the world not being able to contain the books being written about it. It's at this point that we may need to come to the text afresh. You see, we often hear this verse merely quoted to say the passing and obvious statement that Jesus did a lot of regular stuff that isn't in the Gospel. But we already established that such a point is likely not on the front of John's mind. He likely has in view those things which would have been perhaps included in a gospel such as signs, teachings, and the like.
And so even putting aside every meal that Jesus ate and bathe he had as a boy, there is still so much that they would fill too many books for the world to contain. This naturally reads as being one of a spatial limitation. The world itself (the sense of which is as "even the world") cannot contain the number of books that would be written. Certainly that must be an exaggeration. After all, Jesus' public ministry was not all that long. It's not hard to imagine that every even somewhat significant eveny could be contained in a multi-volume set roughly on par with an encyclopedia set. That is, if all you have in view is bar event recording. But the text prevents that idea.
You see, the New Testament can perhaps be summed up as the testimony of the deeds of Christ (Gospels) and the apostolic interpretation of those deeds (Acts-Rev). You have, then, a God-breathed, inerrant, and authoritative declaration of Jesus and the significance of his work. As Scripture it is sufficient and needs nothing to be added to it. And yet, the fact that there exist creeds and confessions, and theologicsl books dating as early as the time of the New Testament church shows us that riches of the implications of Jesus Christ's person and work are so grand that they cannot be exhaustively explored by human language. Thus, John effectively says, "assume, for the sake of argument, that you could exhaustively explore the riches of Jesus Christ's person and work, you'd have a collection of books too bountiful for our world to contain them."
This is good news for us (and Christian book publishers I guess). We will never exhaustively explore Jesus Christ and his work. We will forever praise the Lamb in awe (Rev 22:3). May we ponder the riches of Christ and always be satisfied in wonder.