Some critics (e.g. Godet, Weiss) think that Matthew 5:13-16 are no part of the original sermon, but only an interweaving of sayings which were originally spoken at other times. This is possible, but external evidence exists only in the case of Matthew 5:13 and Matthew 5:15 (for Matthew 5:14 and Matthew 5:16 are peculiar to Matthew); and even in the ease of these verses it is by no means clear (vide infra) that the occasions on which, according to the other Gospels, the sayings were uttered are the more original. Weiss's assertion ('Life,' 2.144), "The remarks in Matthew 5:13-16, bearing on the calling of discipleship,.., cannot belong to the sermon on the mount, carefully as they are there introduced, for the prophesied sufferings of his followers might have made them disloyal," is wholly gratuitous. In fact, the sufferings have been much more strongly spoken of in Matthew 5:11, Matthew 5:12.
The disciples are now addressed directly, and are urged to "walk worthily of the vocation wherewith they are called." The mention of those who have endured persecution leads our Lord to warn his disciples not to faint under persecution in any of its forms; they are but entering on the succession of the prophets; their work is that of purifying and preserving and of illuminating; they must therefore allow their character as disciples to appear, as appear it must if they arc true to their position. There is a purpose in this, namely, that men may see their actions, and glorify their Father which is in heaven.