Let us come also, if you wish, to the circumcision of lips. I think that he would be "uncircumcised in lips" who has not yet ceased from silly talk, from obscene language, who disparages good people, who slanders his neighbors, who instigates quarrels, who promotes false accusations, who sets brothers against themselves by making false statements, who utters vain words, inept words, profane words, shameless words, filthy words, injurious words, wanton words, blasphemous words, and other words that are unworthy of a Christian. But if anyone curbs his mouth from all these things and "orders his words with judgment," if he restrains verbosity, governs his tongue, keeps his words in due bounds, that person deservedly is said to be circumcised in lips. But also those "who speak iniquity on high and stretch out their tongue against heaven," as the heretics do, are to be called uncircumcised and unclean in their lips. But he is circumcised and clean who always speaks the word of God and brings forward sound doctrine fortified with evangelic and apostolic norms. In this way, therefore, also circumcision of lips is given in the church of God.
Source: HOMILIES ON GENESIS 3:5