James 3:2 For we all stumble in many things. If anyone does not stumble in word, he is a perfect man, able also to bridle the whole body.
This seems like such a simple statement, yet when you really think it through it is exactly right. Which shouldn't surprise us, God's Word is ALWAYS right. Put in the most simple terms, if a person is not able to exercise self-control in the way they speak,(whether it be in the face of anger, urge to gossip, desire to slander, or use of profanity) they can not, and will not exercise self-control in other parts of their life.
James talks about our inability to tame the tongue:
James 3:7-8 For every kind of beast and bird, of reptile and creature of the sea, is tamed and has been tamed by mankind. 8 But no man can tame the tongue. It is an unruly evil, full of deadly poison.
This begs the obvious question; if NO MAN can tame the tongue, what is the point of trying or caring if it is tamed?
First, we should care because God does not want us to speak in ways we ought not. He wants us to be self-controled in all aspects of our life; and that is reason enough to strive to tame the tongue.
Secondly, like everything else that is impossible with man, it is possible with Christ to tame the tongue:
Matthew 19:26 But Jesus looked at them and said to them, "With men this is impossible, but with God all things are possible."
Philippians 4:13 I can do all things through Christ who strengthens me.
James gives us a great illustration of small “members” having great responsibility:
James 3:4-5 Look also at ships: although they are so large and are driven by fierce winds, they are turned by a very small rudder wherever the pilot desires. 5 Even so the tongue is a little member and boasts great things. See how great a forest a little fire kindles!