THEOPHYLACT . For as salt preserves flesh, and suffers it not to breed worms, so also the discourse of the teacher, if it can dry up what is evil, constrains carnal men, and suffers not the undying worm to grow up in them. But if it be without saltness, that is, if its virtue of drying up and preserving be gone, with what shall it be salted?
PSEUDO-CHRYSOSTOM . (v. Vict. Ant. in Cat.) Or, according to Matthew, the disciples of Christ are the salt, which preserves the whole world, resisting the rottenness which proceeds from idolatry and sinful fornication. For it may also be meant, that each of us has salt, in as far as he contains in himself the graces of God. Wherefore also the Apostle joins together grace and salt, saying, Let your speech be always with grace, seasoned with salt. (Col. 4:6) For salt is the Lord Jesus Christ, Who was able to preserve the whole earth, and made many to be salt in the earth: and if any of these be corrupted, (for it is possible for even the good to be changed into corruption,) they are worthy to be cast out.
PSEUDO-JEROME . Or otherwise; That salt is saltless which loves the chief place, and dares not rebuke others. Wherefore there follows, Have salt in yourselves, and have peace one with another. That is, let the love of your neighbour temper the saltness of rebuke, and the salt of justice season the love of your neighbour.
GREGORY . (De cura past. iii. c. 22) Or this is said against those whom greater knowledge, while it raises above their neighbours, cuts off from the fellowship of others; thus the more their learning increases, the more they unlearn the virtue of concord.
GREGORY . (Ibid. ii. 4) He also who strives to speak with wisdom should be greatly afraid, lest by his eloquence the unity of his hearers be thrown into confusion, lest, while he would appear wise, he unwisely cut asunder the bonds of unity.
THEOPHYLACT . Or else, he who binds himself to his neighbour by the tie of love, has salt, and in this way peace with his neighbour.
AUGUSTINE . (de Con. 4. 6) Mark relates that the Lord said these things consecutively, and has put down some things omitted by every other Evangelist, some which Matthew has also related, others which both Matthew and Luke relate, but on other occasions, and in a different series of events. Wherefore it seems to me that our Lord repeated in this place discourses which He had used in other places, because they were pertinent enough to this saying of His, by which He prevented their forbidding miracles to be wrought in His name, even by him who followed Him not together with His disciples.