This however is not all; for our first and third Gospels also contain a good deal in common, which is not in Mark, and this looks like another older document, often called 'Q' from the German _Quelle_, meaning '_source_.' It consists chiefly of discourses and parables, though including at least one miracle, that of healing the centurion's servant, and is admitted by most critics to date from before A.D. 50. But here again, it is unlikely for the _whole_ of this earlier document to have been included in two separate Gospels, it is sure to have contained something else besides. Moreover, _as thus restored_ (from Matthew and Luke) it is obviously incomplete. It contains scarcely any narrative to explain how the discourses arose, and of necessity it omits everything in Christ's life which is recorded by St. Mark as well, for this has been already assigned to the so-called Triple Tradition. Therefore when it was complete, it must have contained a good deal more, which may well have been the remainder of our St. Matthew's Gospel. St. Luke would then have only included _a part_ of what St. Matthew wrote, just as they both only included a part of what St. Mark wrote. And the supposed second document would be our St. Matthew's Gospel, just as the supposed Triple Tradition is now thought to be our St. Mark's Gospel. There are difficulties on every theory, but on the whole this seems as satisfactory as any other, and it accounts fairly well for the first two Gospels. But the third Gospel requires further explanation, for besides what is copied from the other two, it contains a good deal of additional matter, such as the parable of the Prodigal Son, which St. Luke must have got from some other source. While he expressly says that _many_ had written before himself; so there were several such sources in existence. And this was only natural, for the Christian religion spread rapidly, and St. Luke himself shows us what its converts were taught. For he says that he only wrote his Gospel to convince Theophilus of the things about which he had already been instructed.[203] Clearly then the course of instruction must have included what the Gospel included; and this was the whole of Christ's life, from His Virgin-Birth to His Ascension. It is hence probable that from the very first Christian teachers had some account of that life. [Footnote 203: Luke 1. 1-4.]