"Luke's" version is the earlier. The correspondences between the two forbid the notion that they are independent. They both begin with a series of blessings, some of which are almost verbally identical. In the middle of each (Luke vi, 27-38, Matthew v, 43-48) there is a striking exposition of the ethical spirit of the command given in Leviticus xix, 18. And each ends with a passage containing the declaration that a tree is to be known by its fruit, and the parable of the house built on the sand. But while there are only twenty-nine verses in the "Sermon on the Plain," there are one hundred and seven in the "Sermon on the Mount"; the excess in length of the latter being chiefly due to the long interpolations, one of thirty verses before, and one of thirty-four verses after, the middlemost parallelism with Luke. Under these circumstances, it is quite impossible to admit that there is more probability that "Matthew's" version of the sermon is historically accurate than there is that Luke's version is so; and they can not both be accurate.
"Luke" either knew the collection of loosely connected and aphoristic utterances which appear under the name of the "Sermon on the Mount" in "Matthew," or he did not. If he did not, he must have been ignorant of the existence of such a document as our canonical "Matthew," a fact which does not make for the genuineness or the authority of that book. If he did, he has shown that he does not care for its authority on a matter of fact of no small importance; and that does not permit us to conceive that he believed the first Gospel to be the work of an authority to whom he ought to defer, let alone that of an apostolic eye-witness.
The tradition of the Church about the second Gospel, which I believe to be quite worthless, but which is all the evidence there is for "Mark's" authorship, would have us believe that "Mark" was little more than the mouth-piece of the apostle Peter. Consequently, we are to suppose that Peter either did not know, or did not care very much for, that account of the "essential belief and cardinal teaching" of Jesus which is contained in the Sermon on the Mount; and, certainly, he could not have shared Dr. Wace's view of its importance.
I thought that all fairly attentive and intelligent students of the Gospels, to say nothing of theologians of reputation, knew these things. But how can any one who does know them have the conscience to ask whether there is "any reasonable doubt"
- Holtzmann ("Die synoptischen Evangelien," 1863, p. 75), following Ewald, argues that the "Source A" ( = the threefold tradition, more or less) contained something that answered to the "Sermon on the Plain" immediately after the words of our present Mark, "And he cometh into a house" (iii, 19). But what conceivable motive could "Mark" have for omitting it? Holtzmann has no doubt, however, that the "Sermon on the Mount" is a compilation, or, as he calls it in his recently published "Lehrbuch" (p. 372), "an artificial mosaic work."