Our Saviour here compares his disciples to salt, thereby denoting their usefulness, salt being one of the most useful things in nature; and pointing out also their duty, which is to season themselves and others with sound doctrine. But hypocritical professors are like unsavory salt; they are neither savory in themselves nor serviceable to others. Our Saviour compares such Christians who have no savor of piety and goodness upon their spirits, to salt, that, having lost its goodness, is neither fit for the land, nor yet for the dunghill: that is, being of a brackish nature, it is wholly unfit to manure the ground, and will rather occasion barrenness than any fruitfulness or increase.
Learn hence, that sincere and serious Christians are and will be as the salt of the earth; that is, good and savory in themselves, and endeavoring by exhortation and good example to season others; but hypocriticl professors and apostatizing Christians will be cast out, and trampled upon as unsavory salt.