Five "Sources"
No other of the four Gospels seems to be made up out of so many and various sources as does the Gospel of St Luke. We can distinguish at least five principal sources, which are quite distinct and independent of each other, and very likely more may have been employed. After all, this is just what we should naturally expect from St Luke's own words in his Preface, for he there tells us that he knew of "many" such documents, and it is certain that, with his desire to produce a really complete history, he would have made use of all which he considered were of a sufficiently authentic character. It would have been, however, quite an impossible task to distinguish these various sources, and to decide with any kind of certainty which portions of the completed whole ought to be assigned to each, were it not for the fortunate circumstance that we happen to possess in its integrity one of the sources employed, and that, too, the most important of all, since it supplies the groundwork of the whole. With its aid the task becomes comparatively an easy one, for we have in it a key to unlock all the problems involved.