Notes on the Bible, by Albert Barnes, , at sacred-texts.com
The regulations respecting vows appropriately follow those given respecting sacrifices, since a large proportion of vows would always relate to the presentation of such offerings. Rules had already been given Lev. 27 for the estimation of things vowed to God. It is probable that this fresh legislation dealing especially with vows made by persons in a state of tutelage, was occasioned by some case of practical difficulty that had recently arisen; and it is addressed by Moses to "the heads of the tribes" Num 30:1, who would in their judicial capacity have to determine questions on these subjects.
There is no provision in the chapter for annulling vows made by boys and young men; from which it has been inferred that the vows of males were in all cases and circumstances binding.
The "vow" was positive; the "bond" negative or restrictive. By a vow a man engaged to dedicate something to God, or to accomplish some work for Him: by a bond he debarred himself from some privilege or enjoyment. A vow involved an obligation to do: a bond, an obligation to forbear doing.
Being in her father's house in her youth - It was not ordinarily until her betrothal or marriage, that the female passed (some suppose by purchase) from the power of her father to that of her husband.
The Lord shall forgive her - i. e., shall remit the obligation. (Compare Kg2 5:18.)
Rather, And if she shall at all be an husband's, and her vows shall be upon her, or a rash utterance of her lips, wherewith she hath bound her soul, etc. The "at all" intimates that the case of a girl betrothed but not yet actually married is here especially contemplated. After betrothal, a woman continued to reside, until the period of her marriage arrived, in her father's house; but her property was from that time forward vested in her husband, and she was so far regarded as personally his, that an act of faithlessness to him was, like adultery, punishable with death Deu 22:23-24. Hence, his right to control her vows even before he actually took her home as his wife.