“If a person vows a vow (i.e., neder: נֶדֶר) to the LORD, or swears an oath (i.e., shevuah: שְׁבוּעָה) to bind himself by a pledge, he shall not break his word. He shall do according to all that proceeds out of his mouth” (Num. 30:2). The Hebrew expression “break his word” literally means “profane his word” (יַחֵל דְּבָרוֹ), that is, to defile the soul by causing it to be inwardly divided, irresolute, and cowardly. After all, breaking your word means violating the integrity of who you are, showing that what you say and what you do are not unified, and this leads to feelings of shame. Your words confess your reality and bring it to life… If you cannot keep your word, your word becomes profane, empty, lost — you become a “stranger to yourself,” unsure of what you intend. “Let your “yes” be yes and your “no” be no; learn to say what you mean and mean what you say (Matt. 5:37).
In the Book of Proverbs we read, “When words are many, transgression is not lacking, but whoever restrains his lips is wise” (Prov. 10:19). The Chofetz Chaim comments: “When people are preparing a telegram, notice how carefully they consider each word before they put it down. That is how careful we must be when we speak.” As James admonishes us: “Let every person be quick to hear, slow to speak, slow to anger” (James 1:19).
Since words represent thoughts, the use of our tongues has to do with how we choose to think… “Think on these things…” We are instructed to “take every thought captive” (αἰχμαλωτίζω, i.e., lead away as a prisoner) to the obedience of Messiah… It is wise to restrain our speech, because, after all, we often have no idea what we are talking about, and therefore our words can become unruly and even dangerous. Whenever we open our mouth to speak, Heaven is listening (Matt. 12:36-37).