HKB
in the early part of the fourth century, writes as follows (Church History, iii, 24, 7-13, translated by McGiffert, in "Nicene and Post-Nicene Fathers," second series, vol. i, p. 153):
"And when Mark and Luke had already published their Gospels, they say that John, who had employed all his time in proclaiming the Gospel orally, finally proceeded to write for the following reason. The three Gospels already mentioned [Matthew, Mark and Luke] having come into the hands of all and into his own too, they say that he accepted them and bore witness to their truthfulness; but that there was lacking in them an account of the deeds done by Christ at the beginning of his ministry. And this indeed is true. For it is evident that the three evangelists recorded only the deeds done by the Saviour for one year after the imprisonment of John the Baptist, and indicated this in the beginning of their account. For Matthew, after the forty days' fast and the temptation which followed it, indicates the chronology of his work when he says: 'Now when he heard that John was delivered up he withdrew from Judea into Galilee.' Mark likewise says: 'Now after that John was delivered up Jesus came into Galilee.' And Luke, before commencing his account of the deeds of Jesus, similarly marks the time, when he says that Herod, 'adding to all the evil deeds which he had done, shut up John in prison.' They say, therefore, that the apostle 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 Saviour during that period; that is, of those which were done before the imprisonment of the Baptist. And this is indicated by him, they say, in the following words: 'This beginning of miracles did Jesus'; and again when he refers to the Baptist, in the midst of the deeds of Jesus, as still baptizing in Ænon near Salim; where he states the matter clearly in the words: 'For John was not yet cast into prison.' John accordingly, in his Gospel, 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. One who understands this can no longer think that the Gospels are at variance with one another, inasmuch as the Gospel according to John contains the first acts of Christ, while the others give an account of the latter part of his life. And the genealogy of our Saviour according to the flesh John quite naturally omitted, because it had been already given by Matthew and Luke, and began with the doctrine of his divinity, which had, as it were, been reserved for him, as their superior, by the divine Spirit."
According to Eusebius, then, John intended to treat the time before the imprisonment of the Baptist as the Synoptists treated the time after that event. We have already noted the element of truth in this observation. Of course it is not the only observation that needs to be made. Much of what John narrates occurred after the imprisonment of the Baptist.
According to Clement of Alexandria, of the close of the second century, who here reports what had been said by his predecessors in Alexandria, John, seeing that "bodily" matters had been treated by the Synoptists, supplemented their work by writing a "spiritual" Gospel. In this testimony also there is no doubt an element of truth. It is true that the Fourth Gospel reproduces certain profound elements in the teaching of Jesus which in the earlier Gospels appear only incidentally.