2 When a man makes a vow to the Lord or takes an oath to obligate himself by a pledge, he must not break his word but must do everything he said.

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.