19 Moreover, so far as regards the Lord's discourses, he does not cease to ascend to the sublimer and more extended utterances of which, from this point also, He delivered Himself. For he inserts a lofty address which the Lord spoke on the occasion when, through Philip and Andrew, the Gentiles expressed their desire to see Him, and which is introduced by none of the other evangelists. There, too, he reports the remarkable words which were spoken again on the subject of the light which enlightens and makes men the children of light. Thereafter, in connection with the Supper itself, of which none of the evangelists has failed to give us some notice, how affluent and how lofty are those words of Jesus which John records, but which the others have passed over in silence!
I may instance not only His commendation of humility, when He washed the disciples' feet, but also that marvellously overpowering and pre-eminently copious discourse which the Lord delivered to the eleven who remained with Him after His betrayer had been indicated by the morsel of bread, and had gone out. It was in this discourse, over which John lingers long, that He said, “He that has seen me, has seen the Father also.” It was in it, too, that He expressed Himself so largely about the Holy Spirit, the Comforter, whom He was to send to them, and about His own glory, which He had with the Father before the world was, and about His making us one in Himself, even as He and the Father are one—not that He and the Father and we should be one, but that we should be one as they are one.
And many other things of a wonderfully sublime order did He utter in that connection. But who can fail to see that to discuss such themes in any manner that would be worthy of them, even if we were competent to do so, is at least not the task which we have undertaken in the present effort? For our object is to help those who are lovers of the Word of God and students of holy truth to understand that, in his Gospel, John was indeed an announcer and preacher of the same Christ, the true and truthful One of whom the other three who have composed Gospels also testified, and to whom the rest of the apostles likewise bore witness, who, although they did not take in hand the construction of written narratives, did at least discharge the kindred service in officially preaching of Him: but that, at the same time, he was borne to far loftier heights in the doctrine of Christ from the very beginning of his book, and that it was but on rare occasions that he kept to the level pursued by the others.
These occasions were the following in particular, namely: first by the Jordan, in reference to the testimony of John the Baptist; secondly, on the other side of the sea of Tiberias, when the Lord fed the multitudes with the five loaves, and walked upon the waters; thirdly, in Bethany, where He had the precious ointment poured over Him by the devotion of a woman of faith. And so he proceeds, until he meets them at the time of the Passion, which, as matter of course, he had to relate in conjunction with them.
But, even in that section, and on the particular subject of the Lord's Supper, which has been left unnoticed by none of them, he has presented us with a much more affluent statement, as if he drew his materials directly from the treasure-store of that bosom of the Lord on which it was his wont to recline. Then, again, [John shows us how] He astonishes Pilate with words of a sublimer import, declaring that His kingdom is not of this world, and that He was born a King, and that He came into the world for this purpose, that He might bear witness to the truth. [It is in this Gospel also that] He withdraws Himself from Mary with some deep mystical intention after His resurrection, and says to her, “Touch me not; for I am not yet ascended to my Father.” It is here, too, that He imparts the Holy Spirit to the disciples by breathing on them giving us thereby to understand that this Spirit who is consubstantial and co-eternal with the Trinity, should not be considered to be simply the Spirit of the Father, but should also be held to be the Spirit of the Son.
Source: The Harmony of the Gospels (New Advent)