The Law concerning Vows

301 And Moses speaketh unto the heads of the tribes of the sons of Israel, saying, 'This 'is' the thing which Jehovah hath commanded: 2 'When a man voweth a vow to Jehovah, or hath sworn an oath to bind a bond on his soul, he doth not pollute his word; according to all that is going out from his mouth he doth.

Matthew Henry's Commentary on Numbers 30:1-2

Commentary on Numbers 30:1-2

(Read Numbers 30:1-2)

No man can be bound by his own promise to do what he is already, by the Divine precept, forbidden to do. In other matters the command is, that he shall not break his words, through he may change his mind.