I. Christ warns us here to beware of false prophets, which come to you in sheep's clothing. There is allusion here, no doubt, to the symbolical garments of the prophets, with which His hearers would be so far familiar, having in their minds John the Baptist's girdle of camel's hair. It is likely enough that sheep's clothing was even more frequently used by them than camel's hair being symbolical at once of their shepherd character and also of innocence and guileless simplicity. Now Christ gives us to understand here that others will come, wearing the prophetic robes, which are easily put on, but not being true shepherds of the sheep, being rather like ravening wolves, who care not save to rend and to kill and to destroy. The sheep's clothing here is not a matter of dress only, but of religious profession and moral bearing, for without some plausible semblance of godliness the false prophet would be easily detected and would soon lose his errand. (1) The false prophets come, they are not sent; they come on their own errands, they are not sent on their mission by God. (2) These false prophets make a wide gate and a broad road for us; and that is perhaps the essential idea of their sheep's clothing.
II. Christ gives us a test by which the false prophet may be tried. "By their fruits," He says, "ye shall know them." By this is meant the truth, not in its mere intellectual aspect, but in its practical results. The proof of a man's grace and truth and godliness is to be sought in two ways. (1) It may be seen first and chiefly in himself. He who calls on us to enter in at the strait gate must show some tokens that he has himself entered in. We must not inquire merely what are his views, but what practical illustration does he give of those views in his life; for if there is no indication that he has been grafted into Christ, how shall I hope to gather grapes of thorns, or good fruit from a corrupt tree? (2) The fruit may be seen in others too. The effect of his teaching may be witnessed in those who hear him. The true shepherd goes before his flock, and they follow him; and if they are all on the narrow road, surely this will be more or less apparent, both in him and in them.
W. C. Smith, The Sermon on the Mount,p. 323.
References: Matthew 7:15-21. Clergyman's Magazine,vol. iii., p. 16; Homiletic Quarterly,vol. i., p. 344.Matthew 7:15-20. J. Oswald Dykes, Manifesto of the King,p. 595.