Salt is good: but if the salt have lost his saltiness, with which will you season it? Have salt in yourselves…
Whatever may be the case with literal salt, Christ is referring to spiritual salt, which undoubtedly, in so far as it consists of a phase of character, may be metamorphosed into its negative or contradictory. Such metamorphic changes of character are possible in two directions; They may be realized upwardly, in bad beings becoming good; or downwardly, in good beings becoming bad. Hatred may be transformed into love, or love into hatred. In either case there is "conversion" from contrary to contrary.
(J. Morison, D. D.)
Parallel VersesKJV: Salt is good: but if the salt have lost his saltness, wherewith will ye season it? Have salt in yourselves, and have peace one with another.