You are the salt of the earth: but if the salt has lost its savor, how shall it be salted? it is thereafter good for nothing, but to be cast out, and to be trodden under foot of men.
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Theophylact of Ochrid
AD 1107
The prophets were sent to one race only, but you are the salt of the whole earth. By your teachings and reproofs you act as an astringent upon the slack and the indolent, so that they will not breed the worms that never die. So do not desist from your astringent reproofs, even if you are reviled or persecuted. Therefore He says:
For if the teacher has become insipid, that is, if he does not give astringent reproofs, but has become soft and lax, "wherewith shall it be salted?" that is, how can this be corrected? So from then on he is cast out from the rank of teacher and is trodden under foot, that is, despised.