Numbers 30:6

Had at all an husband. That is, if she be married. The same would also apply to a betrothed woman still living in her father’s house, for a betrothed husband had rights in connection with his betrothed wife. For example, if she committed adultery, she was stoned to death just as if the marriage had already taken place. She and all her possessions were considered as belonging to her betrothed husband (Deut. 22:23, 24; see also Matt. 1:19, 20).

When she vowed. Literally, “and her vows be upon her.” The vow might have been taken before her betrothal, and had the consent of her father at the time. Now she is betrothed and legally under her betrothed husband’s jurisdiction, and he might require her to renounce her vow.