So also the tongue is a small member, yet it boasts of great things. How great a forest is set ablaze by such a small fire! And the tongue is a fire, a world of unrighteousness. The tongue is set among our members, staining the whole body, setting on fire the entire course of life, and set on fire by hell. For every kind of beast and bird, of reptile and sea creature, can be tamed and has been tamed by mankind, but no human being can tame the tongue. It is a restless evil, full of deadly poison. With it we bless our Lord and Father, and with it we curse people who are made in the likeness of God. From the same mouth come blessing and cursing.
My brothers, these things ought not to be so. 

The tongue can bless or curse, tell the truth or lie. Our tongue, which also represents what we write, is an instrument of evil and for evil, but the tongue of the believer, should be an instrument of righteousness for the glory of God. True worship of God in the Spirit is possible through the tongue; we can praise and exalt the Lord, testify to that worthy name of Jesus, tell others of Him and become spokespersons for eternal blessing. But how quickly, if uncontrolled, the tongue is used in the service of sin. The writer of these verses ends with the obvious - this "ought not be so". Desist from evil, take control of what you say or write; think before speaking.