That which cometh out of the man, that defileth the man.

James 3:2-13 (AMP):
2 For we all often stumble and fall and offend in many things. And if anyone does not offend in speech [never says the wrong things] he is a fully developed character and a perfect man, able to control his whole body and to curb his entire nature.
3 If we set bits in the horses' mouths to make them obey us, we can turn their whole bodies about.
4 Likewise, look at the ships: though they are so great and are driven by rough winds, they are steered by a very small rudder wherever the impulse of the helmsman determines.
5 Even so the tongue is a little member, and it can boast of great things. See how much wood or how great a forest a tiny spark can set ablaze!
6 And the tongue is a fire. [The tongue is a] world of wickedness set among our members, contaminating and depraving the whole body and setting on fire the wheel of birth (the cycle of man's nature), being itself ignited by hell (Gehenna).
7 For every kind of beast and bird, of reptile and sea animal, can be tamed and has been tamed by human genius (nature).
8 But the human tongue can be tamed by no man. It is a restless (undisciplined, irreconcilable) evil, full of deadly poison.
9 With it we bless the Lord and Father, and with it we curse men who were made in God's likeness!
10 Out of the same mouth come forth blessing and cursing. These things, my brethren, ought not to be so.
11 Does a fountain send forth [simultaneously] from the same opening fresh water and bitter?
12 Can a fig tree, my brethren, bear olives, or a grapevine figs? Neither can a salt spring furnish fresh water.
13 Who is there among you who is wise and intelligent? Then let him by his noble living show forth his [good] works with the [unobtrusive] humility [which is the proper attribute] of true wisdom.