Jon D. Payne at Reformation 21 talks about why our words matter.

To be sure, the problem of unwholesome speech is not new. It’s been around for ages. I remember on one occasion, while I was young, my parents washed my mouth out with soap after I had used a bad word, teaching me the valuable lesson that speaking profanity is wrong and unacceptable. No, profanity itself is not new. Corrupt speech has been around since the fall of mankind. But the extensive and wide-ranging use of profanity is a new phenomena in our culture. Even some high profile hipster pastors such as Mark Driscoll have foolishly used salty language from the pulpit, seeking to connect with their younger hearers.
As Christian believers, it is critical that we view this modern profanity epidemic through the lenses of biblical truth. Now more than ever, when it comes to our speech, Christians must be decidedly countercultural.