Matthew 5:13

Ὑμεῖς ἐστε τὸ ἅλας τῆς γῆς· ἐὰν δὲ τὸ ἅλας μωρανθῇ ἐν τίνι ἁλισθήσεται εἰς οὐδὲν ἰσχύει ἔτι εἰ μὴ βληθῆναι ἔξω καὶ καταπατεῖσθαι ὑπὸ τῶν ἀνθρώπων.

You are the salt of the earth, but if the salt becomes tasteless, how can it be made salty again? It is no longer good for anything, except to be thrown out to be trampled by men.