If thou hast done foolishly in lifting up thyself, or if thou hast thought evil, lay thine hand upon thy mouth.
Do not speak, unless you have something peaceful and profitable to say, for words of either pride or sin will produce greater evil and harm. If you are guilty for anything, let your words come out very carefully and very slowly. Let every word count for good.
If your conscience or others correct you for arrogance or wickedness, do not attempt to excuse or justify your sins. Humble yourself, confess your error, and thank the reprover. Do not add to your guilt or shame by opening your mouth and making matters worse.
Your mouth is the vent of your heart and mind. If you have not ruled your thoughts, at least rule your mouth by keeping your folly or wickedness to yourself, lest it harm those around you and spread your sin further. This rule is so valuable that even fools can be thought wise by restraining their words and remaining silent (Pr 17:27-28).
Your tongue can be a flame that fires the course of nature, and it is set on fire of hell (Jas 3:6). Words can be deadly poison (Jas 3:8). You hold the power of death and life in your mouth (Pr 18:21). Much talking always includes sin (Pr 10:19). You will give an account for every idle word (Matt 12:36), including filthy, foolish, and jesting words (Eph 5:3-7).
Doing foolishly in lifting up yourself is to be puffed up with pride and vaunting yourself against authority or over others. When you have foolishly gone this far, the best choice is to stop talking, otherwise provocative things will be said leading to a greater conflict. Pride is the cause of all fights (Pr 13:10), so the fewer arrogant words spoken the better.
Thinking evil is your imagination fantasizing or lusting for forbidden things, assuming evil motives for another person’s actions, purposing to rebel against authority, or related sins of the mind. Even the thought of foolishness is sin (Pr 24:9). If you have failed to rule your thoughts, you can still rule your mouth to keep your evil from becoming public.
Laying your hand over your mouth is a Biblical expression for ending your speech and being silent. Job told his three friends to do this rather than continue their accusations against him (Job 21:5). Job did this himself when confronted by God (Job 40:4). It is what you should do when you feel pride welling up inside or sinful thoughts at work.
The context describes a great king’s authority (Pr 30:31). Wise men will not provoke him with fighting words, for he has the power to destroy (Pr 16:14; 19:12; 20:2; Ec 8:2-5; 10:4). This warning even includes thoughts or private conversations in your bedroom (Ec 10:20). Retorting against authority is folly, but especially against civil rulers (Tit 2:9).
The context also describes the certainty of a fight or war if wrath is pressed (Pr 30:33). A wise man is quick to hear and slow to speak, for he knows that anger does not produce godliness (Jas 1:19-20). He knows that strife in the heart leads to confusion and every evil work, so he refuses to add grievous words to the fire (Pr 15:1; Ja 3:14-18).
The general lesson is valuable. Words take pride and evil imaginations further than intended, provoke others to respond in kind, are impossible to retract, and the damage is difficult to repair, as with offended brothers (Pr 18:19). Therefore, your tongue should be silent in your mouth until and unless there is something peaceful and godly to say.
When pride or evil whet the tongue, its sharp words pierce others, cutting them needlessly and/or starting a war. It is much better to choose the tongue of the wise, dealing grace and health to all who hear (Pr 12:18; 10:20-21; 16:24; Col 4:6; Eph 4:29).
What a peacemaker you could be, if you were always first to lay your hand over your mouth (Pr 15:1; 25:15). But alas, the fire that burns inside often forces release and causes damage (Ps 39:1-3). Be quick to hear and slow to speak to make peace (Jas 1:19-20).
Instead of conceited or corrupt speech, choose the gracious and learned tongue of Jesus Christ, Who spoke better than any man ever (Ps 45:2; Is 50:4; Lu 4:22; Jn 7:46). It is gracious and humble words that win the hearts even of kings (Pr 11:16; 22:11; Ec 10:12).