Numbers 30:13 - Joseph Benson’s Commentary on the Old and New Testaments

To afflict the soul Herself, by fasting, by watching, or the like. And these words are added to show that the husband had this power not only in those vows which concerned himself or his estate, but also in those which might seem only to concern her own person and body; and the reason is, because the wife's person or body being the husband's right, she might not do any thing to the injury of her body without his consent.