A tongue is the mere enunciator of the mind, so when perverse things are said, it's what's on one's mind. Of course, the tongue gets the blame:Ephesians 5:4 (ESV) "Let there be no filthiness nor foolish talk nor crude joking, which are out of place, but instead let there be thanksgiving."
1 Peter 3:10 (ESV) For “Whoever desires to love life and see good days, let him keep his tongue from evil and his lips from speaking deceit..."The tongue is the culprit, but the passage above vindicates it. We are called to keep our tongues from evil and our lips from speaking evil. Where does evil an deceit derive? From the heart.
Luke 6:45 ( ESV) "The good person out of the good treasure of his heart produces good, and the evil person out of his evil treasure produces evil, for out of the abundance of the heart his mouth speaks."The heart is the reflection of what's on one's mind. If the mind is on good, it does good. If it is on evil, it does evil.
Christians, when they are born-again, become new creatures. If the change is efficacious, the mind dwells on new things.
Ezekiel 36:26 ( ESV) "And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh."In essence then, a born-again Christian is changed. God takes away that old heart which reflects on filthy things and foolish talk and wipes it clean. There is reason to be fearful if you are a Christian who has a filthy and foolish mouth. It may be that the seriousness of salvation was made a petty event. Salvation is more than believing and confessing; those things are the prelude to change. If change is not there, perhaps one failed to take Jesus' sacrifice to heart!
One Christian told of his sexual escapades in a braggadocio manner. The non-Christian replied to the bragging with the comment, "I love to hear a good Christian sex story." Of course, he was being sarcastic because the entire concept of filth and Christianity is paradoxical. The man was basically accusing the Christian of being a hypocrite, and indeed he was!
The problem with saying filthy and foolish things is three-fold: (1) God is disappointed, (2) the Christian's mind is on unrighteous things, and (3) the filthy and foolish person is presenting filth and foolishness to someone who doesn't want to hear filth and foolishness.
My analogy is that filthy talk is to the obedient Christian as cigarette smoke is to the non-smoker. Indeed, filth pollutes the air. Just as with cigarettes which can't be blamed, the tongue of the filthy talker is innocent. Just as the smoker is the guilty party with smoking, the mind is the guilty party of those who are filthy.
When I lived in Michigan, there were few born-again Christians. All day long I heard filthy talk and foolishness. Then, when I tried to pray, rather than praise, filth went through my mind. Before I could even pray, I had to deal with my own mind. I was thinking on what I had heard, not because I enjoyed filth, but because I had become acclimated to it! I developed the lung cancer, so to speak, even though I didn't smoke!
Now, when one speaks filthy or says foolish things, remember, the second-hand filth is really offensive to the non-filthy.