Numbers 30:1 And Moses spoke to the heads of the tribes concerning the Children of Israel saying, This is what יהוה has commanded. 2 If a man makes a vow to יהוה or obligates himself by swearing an oath; he will not break his word; he will do all that he said he would do. C-MATS
Question: What does it mean “he will not break his word”? He shall not desecrate his word. A believer’s word is sacred; for him to violate it is a desecration. Everyone must watch their own words, whether spoken, sung, or written. He must do what he says he is going to do. Chumash
Question: What is יהוה giving man the right to do in this verse? By means of an oath, one may either prohibit oneself or require oneself to perform an act. His oath is so strong that a person violating it can suffer the court-imposed penalty of lashes. Chumash
Question: What are the two types of a vow? (a) One can prohibit to himself something that the Torah permits, by saying, for example, “I will not eat bread for thirty days.” (b) One may obligate oneself to bring an optional offering or to perform an optional commandment, such as to tithe to a particular charity. The oath under discussion in this passage is the first type, a voluntarily adopted prohibition (banning yourself from something). With the exception of a vow to perform a commandment [such as (b) above], one cannot use a oath to require oneself to perform an act; for example, if someone were to declare, “I make a oath to go to sleep on time,” it is not binding under the terms of this passage, because you are not prohibiting yourself from doing something. Chumash