Numbers 30 (the entire chapter)
1And Moses spake unto the heads of the tribes concerning the children of Israel, saying, This is the thing which the LORD hath commanded.
2If a man vow a vow unto the LORD, or swear an oath to bind his soul with a bond; he shall not break his word, he shall do according to all that proceedeth out of his mouth.
[SPECIAL PROVISION FOR UNMARRIED WOMEN]
3If a woman also vow a vow unto the LORD, and bind herself by a bond, being in her father's house in her youth; 4And her father hear her vow, and her bond wherewith she hath bound her soul, and her father shall hold his peace at her: then all her vows shall stand, and every bond wherewith she hath bound her soul shall stand. 5But if her father disallow her in the day that he heareth; not any of her vows, or of her bonds wherewith she hath bound her soul, shall stand: and the LORD shall forgive her, because her father disallowed her.
[SPECIAL PROVISION FOR MARRIED WOMEN]
6And if she had at all an husband, when she vowed, or uttered ought out of her lips, wherewith she bound her soul; 7And her husband heard it, and held his peace at her in the day that he heard it: then her vows shall stand, and her bonds wherewith she bound her soul shall stand. 8But if her husband disallowed her on the day that he heard it; then he shall make her vow which she vowed, and that which she uttered with her lips, wherewith she bound her soul, of none effect: and the LORD shall forgive her.
[SPECIAL PROVISION FOR FORMERLY MARRIED WOMEN]
9But every vow of a widow, and of her that is divorced, wherewith they have bound their souls, shall stand against her. 10And if she vowed in her husband's house, or bound her soul by a bond with an oath; 11And her husband heard it, and held his peace at her, and disallowed her not: then all her vows shall stand, and every bond wherewith she bound her soul shall stand. 12But if her husband hath utterly made them void on the day he heard them; then whatsoever proceeded out of her lips concerning her vows, or concerning the bond of her soul, shall not stand: her husband hath made them void; and the LORD shall forgive her.
[EXCEPTION FOR WOMEN OF OATH-BREAKING HUSBANDS]
13Every vow, and every binding oath to afflict the soul, her husband may establish it, or her husband may make it void. 14But if her husband altogether hold his peace at her from day to day; then he establisheth all her vows, or all her bonds, which are upon her: he confirmeth them, because he held his peace at her in the day that he heard them. 15But if he shall any ways make them void after that he hath heard them; then he shall bear her iniquity.
16These are the statutes, which the LORD commanded Moses, between a man and his wife, between the father and his daughter, being yet in her youth in her father's house.
Thus, in general, a woman had the ability to bind herself by an oath/vow, but if there was a man in her life, either a father (if she was unmarried) or a husband (if she was married), then the father/husband could overrule the vow/oath. If he did so the first time he heard it, he would do so without guilt, and he did so later, he would bear the penalty for the woman's breaking the oath.
Notice that God not only gave men authority in the household over their wives and daughters, he also gave them responsibility. They were responsible to pay attention to their wives and daughters, and to repudiate their unlawful oaths/vows.
Sadly, in our day, most societies have - under the influence of Feminism - succombed to French ideas of egalitarianism of the sexes. That is to say, many people (even Christians) seem to imagine that men and women are and ought to be equals. This is contrary to Scripture, as can plainly be seen from the passage above.
There is nothing unjust about Numbers 30. It is God's perfect law and worthy of imitation by modern governments. It establishes, along with other passages, men as the heads of the household. This is both their right and privilege, but also their responsibility. It is no small thing to be responsible for another person.
Nevertheless, women in God's law are not inconsequential. Notice that there are special provisions for women who have lost their men (either by death or divorce), and consequently who stand alone. They are permitted to swear for themselves. When the patriarchy fails, there is a backup.
Although there is nothing ritualistic or especially regional about these provisions, one might try to say that these provisions are for the old testament time period, and that we have new egalitarianism under the New Testament administration.
This is not correct. Recall, for example, Paul's letter to the Ephesians:
Ephesians 5:23 For the husband is the head of the wife, even as Christ is the head of the church: and he is the saviour of the body.
Unlike human patriarchies, there is no need for backup. We will never be left widowed or divorced by Christ. We are constantly under his headship, and we do well to honor that headship with loving obedience.
Praise be to Christ our groom,