As someone who has dealt with this over the years, with mixed success, let me just share what I have learned.
Our first stop is going to be the Bible because Our Lord and the apostles had a lot to say on this.
Matthew 12:33] “Either make the tree good, and its fruit good; or make the tree bad, and its fruit bad; for the tree is known by its fruit. 34] You brood of vipers! how can you speak good, when you are evil? For out of the abundance of the heart the mouth speaks. 35] The good man out of his good treasure brings forth good, and the evil man out of his evil treasure brings forth evil. 36] I tell you, on the day of judgment men will render account for every careless word they utter; 37] for by your words you will be justified, and by your words you will be condemned.”
Matthew 5:21] "You have heard that it was said to the men of old, You shall not kill; and whoever kills shall be liable to judgment.' **22**] But I say to you that every one who is angry with his brother shall be liable to judgment; whoever insults his brother shall be liable to the council, and whoever says, You fool!’ shall be liable to the hell of fire.
33] "Again you have heard that it was said to the men of old, You shall not swear falsely, but shall perform to the Lord what you have sworn.' **34**] But I say to you, Do not swear at all, either by heaven, for it is the throne of God, **35**] or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King. **36**] And do not swear by your head, for you cannot make one hair white or black. **37**] Let what you say be simply Yes’ or `No’; anything more than this comes from evil.
James 1: 26] If any one thinks he is religious, and does not bridle his tongue but deceives his heart, this man’s religion is vain. 27] Religion that is pure and undefiled before God and the Father is this: to visit orphans and widows in their affliction, and to keep oneself unstained from the world.
James 3: 3] If we put bits into the mouths of horses that they may obey us, we guide their whole bodies. 4] Look at the ships also; though they are so great and are driven by strong winds, they are guided by a very small rudder wherever the will of the pilot directs. 5] So the tongue is a little member and boasts of great things. How great a forest is set ablaze by a small fire! 6] And the tongue is a fire. The tongue is an unrighteous world among our members, staining the whole body, setting on fire the cycle of nature, and set on fire by hell. 7] For every kind of beast and bird, of reptile and sea creature, can be tamed and has been tamed by humankind, 8] but no human being can tame the tongue – a restless evil, full of deadly poison. 9] With it we bless the Lord and Father, and with it we curse men, who are made in the likeness of God. 10] From the same mouth come blessing and cursing. My brethren, this ought not to be so. 11] Does a spring pour forth from the same opening fresh water and brackish? 12] Can a fig tree, my brethren, yield olives, or a grapevine figs? No more can salt water yield fresh.
My own prayer has become: Psalm 19: 14] Let the words of my mouth and the meditation of my heart
be acceptable in thy sight,
O LORD, my rock and my redeemer.
These are passages that have really hit home hard with me, and have made me work harder at minding what comes out of my mouth.
