It is not material to enquire when and where this gospel was written; we are sure that it was given by inspiration of God to John, the brother of James, one of the twelve apostles, distinguished by the honourable character of that disciple whom Jesus loved, one of the first three of the worthies of the Son of David, whom he took to be the witnesses of his retirements, particularly of his transfiguration and his agony. The ancients tell us that John lived longest of all the twelve apostles, and was the only one of them that died a natural death, all the rest suffering martyrdom; and some of them say that he wrote this gospel at Ephesus, at the request of the ministers of the several churches of Asia, in opposition to the heresy of Corinthus and the Ebionites, who held that our Lord was a mere man. It seems most probable that he wrote it before his banishment into the isle of Patmos, for there he wrote his Apocalypse, the close of which seems designed for the closing up of the canon of scripture; and, if so, this gospel was not written after. I cannot therefore give credit to those later fathers, who say that he wrote it in his banishment, or after his return from it, many years after the destruction of Jerusalem; when he was ninety years old, saith one of them; when he was a hundred, saith another of them. However, it is clear that he wrote last of the four evangelists, and, comparing his gospel with theirs, we may observe,
1. That he relates what they had omitted; he brings up the rear, and his gospel is as the rearward or gathering host; it gleans up what they has passed by. Thus there was a later collection of Solomon’s wise sayings (Prov. xxv. 1), and yet far short of what he delivered, 1 Kings iv. 32.
2. That he gives us more of the mystery of that of which the other evangelists gave us only the history. It was necessary that the matters of fact should be first settled, which was done in their declarations of those things which Jesus began both to do and teach, Luke i. 1; Acts i. 1. But, this being done out of the mouth of two or three witnesses, John goes on to perfection (Heb. vi. 1), not laying again the foundation, but building upon it, leading us more within the veil. Some of the ancients observe that the other evangelists wrote more of the ta somatika–the bodily things of Christ; but John writes of the ta pneumatika–the spiritual things of the gospel, the life and soul of it; therefore some have called this gospel the key of the evangelists. Here is it that a door is opened in heaven, and the first voice we hear is, Come up hither, come up higher. Some of the ancients, that supposed the four living creatures in John’s vision to represent the for evangelists, make John himself to be the flying eagle, so high does he soar, and so clearly does he see into divine and heavenly things.
– Matthew Henry Commentary