Jamieson, Fausset and Brown on John 21:25

25. And there are many other things which Jesus did--(Compare Joh 20:30, 31).

if ... written every one, I suppose--an expression used to show that what follows is not to be pressed too far.

even the world itself would not hold the books, &c.--not a mere hyperbolical expression, unlike the sublime simplicity of this writer, but intended to let his reader know that, even now that he had done, he felt his materials so far from being exhausted, that he was still running over, and could multiply "Gospels" to almost any extent within the strict limits of what "Jesus did." But in the limitation of these matchless histories, in point of number, there is as much of that divine wisdom which has presided over and pervades the living oracles, as in their variety and fulness.