http://www.rc.net/wcc/readings/johnintro.htm

Some historical reflections from early church sources on John’s Gospel

Irenaeus (130-200 AD), bishop of Lyons, received his account of John, the disciple of the Lord, from Polycarp (69-155 AD), bishop of Smryna, who knew John and had conversed with him. Irenaeus wrote: “John, the disciple of the Lord, who also leant upon his breast, himself also published the gospel in Ephesus, when he was living in Asia.”

Clement of Alexandria (150-215 AD) was a teacher, scripture scholar, and head of the catechetical school in Alexandria, Egypt. He took refuge in Jerusalem during the persecution by the emperor Severus in 201-202. He states that John, who wrote the last account, “composed a spiritual gospel.” “Last of all, John perceiving that the bodily facts had been made plain in the gospel, being urged by his friends, and inspired by the Holy Spirit, composed a spiritual gospel.”

The Muratorian Canon, a document written in Rome and dating 180-200 AD, contains a list of the books of the New Testament. It explains how the Gospel of John came to be written:

The fourth Gospel is that of John, one of the disciples. When his fellow disciples and bishops pleaded with him, he said, “Fast with me for three days, and then we’ll tell each other whatever may be revealed to any of us.” That very night it was revealed to Andrew, one of the apostles, that John should write everything in his own name as they remembered them.
As a result, although different points are taught to us in the various books of the Gospels, there is no difference as regards the faith of believers. In all of them under [the influence of] one imperial Spirit, everything is told which concerns the Lord’s birth, his suffering, his resurrection, his conduct with his disciples, and his twofold coming: the first in the humiliation of rejection, which is now past, and the second in the glory of royal power, which is still in the future.
What a marvel it is, then, that John presents these various things so consistently in his letters, too! He says in his own person, “What we have seen with our eyes, heard with our ears, and our hands have handled, that have we written.” For in this way he testifies that he is not only the eye-witness, but also the hearer. Besides that, he is also the historian of all the wondrous facts concerning the Lord in their order.

Eusebius of Caesarea (260-340), a scholar and church historian, comments on the difference between John’s Gospel and the other three accounts written by Matthew, Mark, and Luke :

Matthew at first preached to the Hebrew people. The day came when he had to leave them and to go to other nations. Before he went he set down his story of the life of Jesus in Hebrew, “and thus compensated those whom he was obliged to leave for the loss of his presence.” After Mark and Luke had published their gospels, John was still preaching the story of Jesus orally. “Finally he proceeded to write for the following reason. The three gospels already mentioned having come into the hands of all and into his hands too, they say that he fully accepted them and bore witness to their truthfulness; but there was lacking in them an account of the deeds done by Christ at the beginning of his ministry…. They therefore say that John, being asked to do it for this reason, gave in his gospel an account of the period which had been omitted by the earlier evangelists, and of the deeds done by the Savior during that period; that is, of the deeds done before the imprisonment of John the Baptist…. John therefore records the deeds of Christ which were performed before the Baptist was cast into prison, but the other three evangelists mention the events which happened after that time…. The Gospel according to John contains the first acts of Christ, while the others give an account of the latter part of his life” (Eusebius, The Ecclesiastical History 5:24).

Augustine of Hippo (345-430 AD ), in his Harmony of the Gospels, contrasts John with the other three evangelists – Matthew, Mark, and Luke.

In the four Gospels, or rather in the four books of the one Gospel, Saint John the apostle, not undeservedly in respect of his spiritual understanding compared to the eagle, has elevated his preaching higher and far more sublimely than the other three… For the other three evangelists walked with the Lord on earth but this evangelist, as if he disdained to walk on the earth, just as in the very opening of his discourse he thundered on us, soared not only above the earth and above the whole compass of air and sky, but even above the whole army of angels and the whole order of invisible powers, and reached to him by whom all things were made, saying, “in the beginning was the Word, and the Word was with God, and the Word was God” (John 1:1). (in his Harmony of the Gospels 1.6.9)