Out of my mouth

I've been trying to listen to John Piper's Desiring God podcast over the past couple of days.  It's kind of hard to listen and understand him when I'm doing other things, but I pick up things here and there.  He briefly touched on the following two weeks ago.

 

In the New Testament, Matthew 15.18 says "But the things that come out of the mouth come from the heart."  It's interesting to me that he doesn't qualify it by saying "some of the things."  Just says "the things."  And I've been thinking.  Thinking about the things that come ouf of my mouth and the things that come out of the mouths of other Christians.  If a "Christian organization" verbally attacks someone in the media, what's in their heart?  I'f I'm driving with a friend and he berates, the driver who cut him off, what's in his heart?  If I'm playing racquetball with a friend and they call themselves stupid, what's in their heart?  If I find myself calling somebody a moron, what's in my heart?  Or more importantly, what's not?  Why do we grumble and complain?