2 If a man vow a vow to Jehovah, or swear an oath to bind his soul with a bond, he shall not break his word; according to all that hath gone out of his mouth shall he do.

Matthew Henry's Commentary on Numbers 30:2

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.