See the Matthew 5:13 note; Mark 9:49-50 notes.
Salt is good - It is useful. It is good to preserve life and health, and to keep from putrefaction.
His savour - Its saltness. It becomes tasteless or insipid.
Be seasoned - Be salted again.
Fit for the land - Rather, it is not fit “for land,” that is, it will not bear fruit of itself. You cannot sow or plant on it.
Nor for the dunghill - It is not good for manure. It will not enrich the land,
Cast it out - They throw it away as useless.
He that hath ears ... - See Matthew 11:15. You are to understand that he that has not grace in his heart; who merely makes a profession of religion, and who sustains the same relation to true piety that this insipid and useless mass does to good salt, is useless in the church, and will be rejected. “Real” piety, true religion, is of vast value in the world. It keeps it pure, and saves it from corruption, as salt does meat; but a mere “profession” of religion is fit for nothing. It does no good. It is a mere encumbrance, and all such professors are fit only to be cast out and rejected. All such “must” be rejected by the Son of God, and cast into a world of wretchedness and despair. Compare Matthew 7:22-23; Matthew 8:12; Matthew 23:30; Matthew 25:30; Revelation 3:16; Job 8:13; Job 36:13.