The tongue is a small member, yet it boasts of great exploits. How great a forest is set ablaze by a small fire! And the tongue is a fire. The tongue is placed among our members as a world of iniquity; it stains the whole body, sets on fire the cycle of nature, and is itself set on fire by hell. For every species of beast and bird, of reptile and sea creature, can be tamed and has been tamed by the human species, but no one can tame the tongue—a restless evil, full of deadly poison. With it we bless the Lord and Father, and with it we curse those who are made in the likeness of God. From the same mouth come blessing and cursing. My brothers and sisters, this ought not to be so. Does a spring pour forth from the same opening both fresh and brackish water? Can a fig tree, my brothers and sisters, yield olives, or a grapevine figs? No more can salt water yield fresh. (James 3:5-12, NRSV)
The tongue is a little member, and boasteth great things. Behold, how great a matter a little fire kindleth! And the tongue is a fire, a world of iniquity: so is the tongue among our members, that it defileth the whole body, and setteth on fire the course of nature; and it is set on fire of hell. For every kind of beasts, and of birds, and of serpents, and of things in the sea, is tamed, and hath been tamed of mankind: But the tongue can no man tame; it is an unruly evil, full of deadly poison. Therewith bless we God, even the Father; and therewith curse we men, which are made after the similitude of God. Out of the same mouth proceedeth blessing and cursing. My brethren, these things ought not so to be. Doth a fountain send forth at the same place sweet water and bitter? Can the fig tree, my brethren, bear olive berries? Either a vine, figs? So can no fountain both yield salt water and fresh. (James 3:5-12, KJV)
Ask any politician who's ever experienced a gaffe: your tongue may be little, but it can get you in a lot of trouble. Here, James tells Christians that they shouldn't use their mouths for dual purposes. Don't worship God with your lips and then slag off his people in the next breath. It's just rude.