In Psalm 34, David gives instruction as to what it means to fear the Lord. The first aspect he lists is that we are to fear the Lord with our tongues: "Keep your tongue from evil and your lips from speaking deceit. — Psalm 34:13".

For further meditation on keeping your tongue from evil, please consider the following quote from W. S. Plumer and the brief excerpt from Richard Baxter.

“Speaking becomes sinful when it is hasty, rash, continual, unseasonable, excessive, clamorous, senseless, unchaste, indelicate, impure, filthy, prevaricating, quibbling, deceitful, lying, slanderous, tattling, babbling, backbiting, detractive, reproachful, opprobrious, flattering, seductive, betraying confidence, revealing secrets, awakening groundless suspicions, talebearing, news-carrying, railing, reviling, boatsful, scornful, desperate, murmuring, foolish, egotistical, vain, proud, malignant, bitter, resentful, cursing, profane, or blasphemous.”

— W.S. Plumer[1]

30 Sins of the Tongue

Extracted from The Practical Works of the Rev. Richard Baxter. Vol. 3

 Direct. iii. ‘Understand and remember what are the sins of the tongue to be avoided.’ And they are very many, and many of them very great: the most observable are these,—

1. (Not to say any more of the sins of omission; because it is easy to know them, when I have named the duties, which are done or omitted,) among the sins of commission, the first that I shall name is blasphemy, as being the greatest; which is the reproaching of God: to speak contemptuously of God, or to vilify him, or dishonour him by the denying of his perfections, and to debase him by false titles, doctrines, images, resemblances, as likening him to man in any of our imperfections; any thing that is a reproaching of God is blasphemy. Such as Rabshakeh used when he threatened Hezekiah; and such as infidels and heretics use, when they deny his omnipresence, omniscience, government, justice, particular providence or goodness: and affirm any evil of him, as that he is the author of sin, or false of his word, or that he governeth the world by mere deceit, or the like.
2. Another sin of the tongue is false doctrine, or teaching things false and dangerous as from God: if any falsely say, he had such or such a point by divine inspiration, vision, or revelation, that maketh him a false prophet. But if he only say falsely, that this or that doctrine is contained in the Scripture, or delivered by tradition to the church, this is but to be a false teacher; which is a sin greater or less according to the aggravations hereafter mentioned.
3. Another of the sins of the tongue is an opposing of godliness indirectly, by false application of true doctrine, and an opposing of godly persons for the sake of godliness, and cavilling against particular truths and duties of religion: or indirectly opposing the truth or duty under pretence of opposing only some controverted mode or imperfection in him that speaketh or performeth it: a defending of those points and practices which would subvert or undermine religion: a secret endeavour to make all serious godliness seem a needless thing. There are many that seem orthodox, that are impious and malicious opposers of that truth in the application, which themselves do notionally hold, and positively profess.
4. Another great sin of the tongue is the profane deriding of serious godliness, and the mocking, and jesting, and scorning at godly persons as such; or scorning at some of their real or supposed imperfections, for their piety sake, to make them odious, that piety through them might be made odious. When men so speak, that the drift and tendency of their speech is to draw men to a dislike of truth or holiness; and their mocks or scorns at some particular opinion, or practice, or mode, doth tend to the contempt of religion in the serious practice of it. When they mock at a preacher of the Gospel, for some expressions or imperfections, or for truth itself, to bring him and his doctrine into contempt: or at the prayers and speeches of religious persons to the injury of religion.
5. Another great sin of the tongue is unjustly to forbid Christ’s ministers to preach his Gospel, or speak in his name; or to stand up against them and contradict, resist, and hinder them in the preaching of the truth: and as Gamaliel calls it, “to fight against God.” Yet thus they did by the apostles, “When they had called the apostles and beaten them, they commanded that they should not speak in the name of Jesus, and let them go.” So Acts 4:18, 19. “And they called them and commanded them not to speak at all, nor teach in the name of Jesus: but Peter and John answered and said unto them, whether it be right in the sight of God, to hearken unto you more than unto God, judge ye; for we cannot but ‘speak the things which we have seen and heard.” “Who both killed the Lord Jesus, and their own prophets, and have persecuted us; and they please not God and are contrary to all men. Forbidding us to speak to the Gentiles that they might be saved, to fill up their sins always: for the wrath is come upon them to the uttermost.” As Dr. Hammond paraphraseth it, ‘And this generally is the ground of their quarrel to us, that in spite of their prohibition, we preach to the Gentiles.’—
6. Another sin of the tongue is profane swearing either by God or by creatures: and also all light and unreverent use of the name and attributes of God, of which more afterwards.
7. Much more is perjury or forswearing a most heinous sin, it being an appealing to God, the author and defender of truth, to bear witness to an untruth, and to judge the offender; and so a craving a vengeance from God.
8. Lying also is a great and common sin of the tongue: of which more anon.
9. Another sin of the tongue is hypocritical dissembling, which is worse than mere lying: when men’s tongues agree not with their hearts, but speak good words in prayer to God, or conference with men, to cover evil intentions or affections, and to represent themselves to the hearers as better than they are.
10. Another is ostentation or proud boasting, either of men’s wit and learning, or greatness, or riches, or honour, or strength, or beauty, or parts, or piety, or any thing that men are proud of? As the faithful “do make their boast in God,” and in the “cross of Christ,” by which “they are crucified to the world.” So the covetous “boast themselves in the multitude of their riches,” and the “workers of iniquity boast themselves against the righteous, and the proud do triumph and speak hard things.” “Even against the Lord,” do they boast, in their boasting against his people. So far as pride prevaileth with men, they are apt to “boast themselves to be somebody.” Either openly as the more foolish do, or cunningly by the help of fair pretences, as the more ingenious proud ones do.
11. Another sin of the tongue is unseasonable speaking of common things when holy things should be preferred; as on the Lord’s day, or at the time of public worship, or when the company, occasion or opportunity call for holy speeches; worldlings are talking, as Saul, of their asses, when they should talk of a kingdom. To speak about your callings and common affairs is lawful, so it be moderately and in season; but when you talk all of the world and vanity, and never have done, and will scarce have any other talk in your mouths, and even on God’s day will “speak your own words,” this is profane and sinful speaking.
12. Another common sin of the tongue is a tempting and persuading others to sin, enticing them to gluttony, drunkenness, wantonness, fornication, or any other crime: as men that “not only do the same, but have pleasure in them that do them.” This is to be the instruments and servants of the devil, and most directly to do his work in the world. The same I may say of unjust excusing, extenuating or defending the sins of others, or commanding, alluring, affrighting, or encouraging them thereto.
13. Another is a carnal manner of handling the sacred things of God, as when it is done with lightness, or with unsuitable curiosity of words, or in a ludicrous, toyish manner, especially by the preachers of the Gospel themselves; and not with a style that is grave and serious, agreeable to the weight and majesty of the truth.
14. Another is an imprudent, rash, and slovenly handling of holy things: when they are spoken of so ignorantly, unskillfully, disorderly, or passionately, as tendeth to dishonour them, and frustrate the desired good success.
15. Another sin of the tongue is the reviling or dishonouring of superiors: when children speak unreverently and dishonourably to or of their parents; or subjects of their governors; or servants of their masters, either to their faces, or behind their backs. “They are not afraid to speak evil of dignities.”
16. Another is the imperious contempt of inferiors, insulting over them, provoking and discouraging them. “Fathers provoke not your children to wrath.”
17. Another sin of the tongue is idle talk and multitude of useless words; a babbling loquacity, or unprofitableness of speech; when it is speech that tendeth to no edification, any good use for mind, or body, or affairs.
18. Another sin is foolish talk, or jesting in levity and folly, which tendeth to possess the minds of the hearers with a disposition of levity and folly, like the speakers. “Foolish talking and jesting are things not convenient.” Honest mirth is lawful; and that is the best which is most sanctified, as being from a holy principle, and about a holy matter, or to a holy end: “as rejoicing in the Lord always.” “If any be merry let him sing psalms.” But such a light and frothy jesting, as is but the vent of habitual levity by idle words, is not allowable. But especially those persons do most odiously abuse their tongues and reason, who counterfeit idiots or fools, and use their wit to cover their jests with a seeming folly, to make them the more ridiculous, and make it their very profession to be the jesters of great men. They make a trade of heinous sin.
19. Another sin is “filthy speaking;” obscene and ribald talk; which the apostle calls “corrupt or rotten communication;” when wanton, filthy minds do make themselves merry with wanton, filthy speeches. This is the devil’s preparative to whoredom and all abominable uncleanness: for when the tongue is first taught to make a sport of such filthy sins, and the ear to be delighted in it, or be indifferent to it, there remaineth but a small step to actual filthiness.
20. Another sin of the tongue is cursing; when men wish some mischief causelessly or unwarrantably to others. If you speak but in passion or jest, and desire not to them in your hearts the hurt which you name, it is nevertheless a sin of the tongue, as it is to speak blasphemy or treason in a passion or in jest: the tongue must be ruled as well as the heart. But if really you desire the hurt which you wish them, it is so much the worse. But it is worst of all, when passionate, factious men will turn their very prayers into cursings, calling for fire from heaven, and praying for other men’s destruction or hurt; and pretending Scripture examples for it; as if they might do it unwarrantably, which others have done in other cases in a warrantable manner.
21. Slandering is another sin of the tongue: when out of malice and ill will, men speak evil falsely of others to make them odious or do them hurt: or else through uncharitable credulity, do easily believe a false report, and so report it again to others; or through rashness and unruliness of tongue, divulge it, before they try it, or receive either just proof, or any warrantable call to mention it.
22. Another sin is backbiting and venting ill reports behind men’s backs, without any warrant. Be the matter true or false, as long as you either know it not to be true, or if you do, yet vent it to make the person less respected, or at least without a sufficient cause, it is a sin against God, and a wrong to men.
23. Another sin is rash censuring, when you speak that evil of another, which you have but an uncharitable surmise of; and take that to be probable which is but possible, or that to be certain which is but probable against another.
24. Another sin is railing, reviling, or passionate, provoking words, which tend to the diminution of charity, and the breach of peace, and the stirring up of discord, and of a return of railing words from others, contrary to the love, and patience, and meekness, and gentleness which become saints.
25. Another sin is cheating, deceiving, over-reaching words: when men use their tongues to defraud their neighbours, in bargaining for their own gain.
26. Another sin of the tongue is false witness-bearing, and false accusing; a sin which cries to God for vengeance, who is the justifier of the innocent.
27. Another sin of the tongue is the passing an unrighteous sentence in judgment: when rulers absolve the guilty or condemn the just, and call evil good, and good evil, and say to the righteous, “Thou art wicked.”
28. Another sin of the tongue is flattery; which is the more heinous by how much more hurtful. And it is most hurtful, 1. When it tendeth to delude men in the greatest things, even the state of their souls. The flattery of a preacher that deceiveth men as in the name of Christ, is of all other flattery the most pernicious: to make the unregenerate believe that they are regenerate, and the ungodly to believe that they are godly, and the unjustified to believe that they are justified, and the children of satan to believe that without conversion they may be saved; to make a worldling, a swearer, a glutton, a drunkard, a fornicator, a formal hypocrite, or a hater of holiness, believe that such as he may come to heaven without the sanctifying, renewing work of the Holy Ghost; this is the most eminent service of the devil that the tongue of any man can do him, except it be the very open opposers of religion. As the devil useth more to flatter men to hell, than to frighten them thither, so do his ministers and instruments. And all doctrines of libertinism and looseness, which warrant men to do evil and to neglect a holy life, are of the two a more dangerous way of flattery, than that which consisteth but in misapplication. Thus also carnal friends do use to flatter a sinner into presumption and false hopes, when they see him convinced of his sin and misery, and say, ‘Trouble not yourself; God is merciful, and you have lived well, and been a good neighbour, and done nobody harm, and if such as you be not saved, God help a great many.’ Thus when a convinced sinner is striving to get out of the devil’s snares, the servants of satan rock him asleep again, by false and flattering speeches and deceit. 2. Flattering is pernicious when it tendeth to the hurt of many: as when rulers are deceived and perverted by it to the destruction of the people and themselves. “A lying tongue hateth those that are afflicted by it, and a flattering mouth worketh ruin.”
29. Another sin is a jeering, mocking, deriding, or scorning at others, either for their infirmities of body or mind, or for their virtues, or through envy and malice, or pride, or a custom of deriding, scornful speech. “Scorners delight in scorning,” especially when sinners scorn at the reproofs and counsels of the godly, and cast them all back into their faces with contempt: for he that “reproveth a scorner getteth himself a blot.” “A scorner loveth not one that reproveth.”
30. Another tongue-sin is idolatry or false worship: the praise of idols, or praying to them, or making songs, or speeches, or disputes for them: as also the false worship of the true God. These among others are the sins of the tongue to be avoided. No wonder if there be yet more, for the “tongue is ‘ὁ κόομος τής ἀδικίας,’ a world of iniquity.”[2]

[1] W. S. Plumer, Studies in the Book of Psalms, pg. 421

[2]  Baxter, Richard, William Orme. The Practical Works of the Rev. Richard Baxter. Vol. 3. London: James Duncan, 1830. Print.