But those things which proceed out of the mouth
Meaning not material things, as spittle, vomit but, as it follows, which
come forth from the heart:
are first conceived and formed there, and then come forth from thence, and are expressed by the mouth; as all idle words, foolish talking, filthy jesting, unsavoury communication, and every word that is rotten and corrupt, or which is done in the life and conversation;
and they defile the man:
the heart is the corrupt fountain from whence all moral defilement flows; and sinful words and actions are the impure streams, which spring from thence, and increase the moral pollution of human nature.