When we make a covenant with God it is a very serious matter to enter into. It would be better for a man not to make a promised to God than to make one and not keep it. (Ecclesiastes 5:5)
The Israelites would make a promise to God that they would do particular things. And sometimes they would make a promise not to do a particular thing. Sometimes they would promises a special sacrifice to God or a person would promise to fast for a certain time. If a man made a promise, then he was bound to that promise. But there were different rules for the women, because they lived under the authority of men. The Father had authority over his unmarried daughter and the husband had authority over his wife.
If an unmarried daughter made a promise, then the Father could cancel that promise. Likewise if a wife mad a promise, then the husband could cancel that promise. Even a promise that she had made before they were married. If a father or husband did not hear the woman make the promise, then when hearing about it he would either have to confirm or cancel it. This cancelation had to be made on the day that he heard of the promise.
The father or the husband might not have known about the promise. Other people might have told them about it. But when they heard about it, they could cancel it. However, they had to cancel it quickly, on the same day when they heard about it first.
It is important for us to give a lot of consideration before we make a promise to God. We should never make a promise to God if we do not intend to keep it.