"Sources" peculiar to St Luke
The two sources of which we have already spoken were common both to St Matthew and St Luke, and between them provide the whole, or nearly the whole, of the matter which is given by both Evangelists; but St Luke had other and special sources at his command which were apparently not known to the other Evangelist, and which form the distinctive portion of his Gospel. You may find evidence of the use of one such special source in the long insertion of narrative matter which breaks into the framework of the Marcan story between the ninth and the eighteenth chapters. This "great insertion," as it is often called, is the despair of those harmonists who insist on treating each of the Gospels as being an orderly and strictly chronological statement of the events of our Lord's life. The occurrences there recorded refuse altogether to fit in with the arrangement found in the other Evangelists unless much ingenuity and some little violence be brought to bear. It is probable that the whole came into St Luke's hands as an independent collection of Gospel material, and that he has incorporated it almost as it stood, giving it only a very slight connection with the main thread of his story, and not attempting to harmonise the two sources so far as chronological exactness is concerned.
Interest of this "Source"
This particular source is one of peculiar interest, and contains portions of the Gospel story which we shall all of us feel we should ill do without -- such as, to give one or two examples, the Parables of the Good Samaritan and the Prodigal Son. It is this portion of his Gospel which gives the character of wide human sympathy which is so conspicuous in St Luke's work, and it is consequently a question of special interest to ask whence it was, and from what teacher, that words which have had so marvellous an influence on the world's development were originally recorded.
Who was Author of this "Source"?
Very possibly we may never be able to answer this question with anything approaching certainty, but there are a few points which may, perhaps, afford matter for a more or less plausible conjecture, and it may serve to interest you, and at the same time to give greater distinctness to what I am saying, if we pause a few moments in order to subject these indications, faint and inconclusive as they must be allowed to be, to a brief examination.
Philip the Deacon
The name which I am going to suggest to you as being the one of our Lord's disciples who formed this collection and gave it to St Luke is Philip the Deacon. He is given the title of Evangelist in a very marked way by St Luke himself being the only person to whom that title is applied in the New Testament; and although we have no right to assume that the word implies actual authorship, still it does suggest at the very least a certain marked familiarity with the actual facts of the Gospel story by which he was distinguished among the other officials of the Church in Palestine. There exists, too, an Apocryphal Gospel of early date, which bears the name of Philip; and these Apocryphal writings in the second and third centuries nearly always imply the earlier existence of an authentic document, whose name they adopt, and for which it is desired that they shall be mistaken. St Luke was resident for two years in Philip's house at Caesarea about the year 57, and it can scarcely be doubted that it was from him that he obtained much of the information on the beginnings of the Church which is to be found in the book of the Acts, and especially the details there recorded about Philip's own evangelistic work in Samaria. Nothing, therefore, can be more probable than that he should at the same time have obtained any material that Philip may have had to give him for the enrichment of his Gospel also. The mention of Samaria, too, suggests the fact that this particular portion of the Gospel shows a quite peculiar interest in Samaria and the Samaritans -- almost every instance in which the Samaritans are mentioned by the Synoptic writers being limited to this short part of St Luke. These small indications are, as will be seen, very far from amounting to a demonstration, but still, in the absence of any more definite information, they may have their value in providing an interesting conjecture and in assisting the memory to keep this one of St Luke's sources clear and distinct.