A.T. Robertson Commentary John 21:25

"And there are also many other things which Jesus did, the which if they should be written every one, I suppose that even the world itself would not contain the books that should be written." — John 21:25 (ASV)

If they should be written every one (εαν γραφητα καθ' εν). Condition of the third class with εαν and present passive subjunctive of γραφω, "If they should be written one by one" (in full detail).

I suppose (οιμα). Note change back to the first person singular by the author.

Would not contain (ουδ' αυτον τον κοσμον χωρησειν). Future active infinitive in indirect discourse after οιμα. This is, of course, natural hyperbole, but graphically pictures for us the vastness of the work and words of Jesus from which the author has made a small selection (20:30f.) and by which he has produced what is, all things considered, the greatest of all the books produced by man, the eternal gospel from the eagle who soars to the very heavens and gives us a glimpse of the glory of God in the face of Jesus Christ.