Numbers 30:2 - Matthew Poole's English Annotations on the Holy Bible

A man; which notes both the sex, as appears by Numbers 30:3, and the age, that he be grown up; for none can be so weak as to think the vow of a young child would bind it. A vow, i.e. a simple Vow to do something possible and lawful. Unto the Lord; to the honour and service of God. Or swear an oath; confirm his vow by an oath. To bind his soul with a bond; to restrain himself from something otherwise lawful, as suppose from such a sort of meat or drink; or to oblige himself to the performance of something otherwise not necessary, is to observe a private day of fasting. He shall not break his word, Heb. not pollute or profane his word, as the same phrase is used, Psalms 55:20, Psalms 89:34, i.e. not render his word, and consequently himself, profane, or vile and contemptible in the eyes of others. According to all that proceedeth out of his own mouth; and that without delay, Deuteronomy 23:21 Ecclesiastes 5:4, provided the thing be not unlawful and forbidden by God, Acts 23:14; for it is an idle conceit that a man can give away God's right, or that he can make void God's commands by his own vows, which was the dotage of the Pharisees, Mark 6:23,26.