Hilary of Poitiers
Catena Aurea · Matthäusevangelium 5
Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men.
There may be here seen a propriety in our Lord’s language which may be gathered by considering the Apostles’ office, and the nature of salt. This, used as it is by men for almost every purpose, preserves from decay those bodies which are sprinkled with it; and in this, as well as in every sense of its flavour as a condiment, the parallel is most exact. The Apostles are preachers of heavenly things, and thus, as it were, salters with eternity; rightly called the salt of the earth, as by the virtue of their teaching, they, as it were, salt and preserve bodies for eternity.