Verse 31. "That ye might believe" - What is here recorded is to give a full proof of the Divinity of Christ; that he is the promised Messiah; that he really suffered and rose again from the dead; and that through him every believer might have eternal life.
"Life" - Several MSS., versions, and fathers read eternal life, and this is undoubtedly the meaning of the word, whether the various reading be admitted or not.
GROTIUS has conjectured that the Gospel, as written by St. John, ended with this chapter, and that the following chapter was added by the Church of Ephesus. This conjecture is supported by nothing in antiquity. It is possible that these two last verses might have formerly been at the conclusion of the last chapter, as they bear a very great similarity to those that are found there; and it is likely that their true place is between the 24th and 25th verses of the succeeding chapter; ; with the latter of which they in every respect correspond, and with it form a proper conclusion to the book. Except this correspondence, there is no authority for changing their present position.
After reading the Gospel of John, his first Epistle should be next taken up: it is written exactly in the same spirit, and keeps the same object steadily in view. As John's Gospel may be considered a supplement to the other evangelists, so his first Epistle may be considered a supplement and continuation to his own Gospel. In some MSS. the epistles follow this Gospel, not merely because the transcribers wished to have all the works of the same writer together, but because there was such an evident connection between them. The first Epistle is to the Gospel as a pointed and forcible application is to an interesting and impressive sermon.