What goes into the mouth does not make a man unclean; it is what comes out of the mouth that makes him unclean. What comes out of the mouth comes from the heart, and this defiles a person. For from the heart comes evil intentions: murder, adultery, fornication, theft, perjury, slander. These are the things that make a man unclean.
As I was doing my reading this morning, this passage jumped out at me, and I actually thought about writing on it today. Alas, the Rev. Paul McClain also beat me to it on Cyberbrethren:
Put Up a Guard at the Door of My Lips! Thoughts on the Eighth Commandment