
Jerome
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.
The illustration is taken from husbandry. Salt, though it be necessary for seasoning of meats and preserving flesh, has no further use. Indeed we read in Scripture of vanquished cities sown with salt by the victors, that nothing should thenceforth grow there.