If 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.

King James Translators' Notes

break: Heb. profane

Jamieson-Fausset-Brown Bible Commentary

2. If a man vow a vow unto the Lord-A mere secret purpose of the mind was not enough to constitute a vow; it had to be actually expressed in words; and though a purely voluntary act, yet when once the vow was made, the performance of it, like that of every other promise, became an indispensable duty-all the more because, referring to a sacred thing, it could not be neglected without the guilt of prevarication and unfaithfulness to God.

he shall not break his word-literally, "profane his word"-render it vain and contemptible (Ps 55:20; 89:34). But as it would frequently happen that parties would vow to do things which were neither good in themselves nor in their power to perform, the law ordained that their natural superiors should have the right of judging as to the propriety of those vows, with discretionary power to sanction or interdict their fulfilment. Parents were to determine in the case of their children, and husbands in that of their wives-being, however, allowed only a day for deliberation after the matter became known to them; and their judgment, if unfavorable, released the devotee from all obligation [Nu 30:3-8].

Matthew Henry's Concise Commentary

30:1,2 No man can be bound by his own promise to do what he is already, by the Divine precept, forbidden to do. In other matters the command is, that he shall not break his words, through he may change his mind.

Matthew Henry's Whole Bible Commentary

Chapter 30

In this chapter we have a law concerning vows, which had been mentioned in the close of the foregoing chapter. I. Here is a general rule laid down that all vows must be carefully performed (v. 1, 2). II. Some particular exceptions to this rule. 1. That the vows of daughters should not be binding unless allowed by the father (v. 3-5). Nor, 2. The vows of wives unless allowed by the husband (v. 6, etc.).

Verses 1-2

This law was delivered to the heads of the tribes that they might instruct those who were under their charge, explain the law to them, give then necessary cautions, and call them to account, if there were occasion, for the breach of their vows. Perhaps the heads of the tribes had, upon some emergency of this kind, consulted Moses, and desired by him to know the mind of God, and here they are told it: This is the thing which the Lord has commanded concerning vows, and it is a command still in force.

1. The case supposed is that a person vows a vow unto the Lord, making God a party to the promise, and designing his honour and glory in it. The matter of the vow is supposed to be something lawful: no man can be by his own promise bound to do that which he is already by the divine precept prohibited from doing. Yet it is supposed to be something which, in such and such measures and degrees, was not a necessary duty antecedent to the vow. A person might vow to bring such and such sacrifices at certain times, to give such and such a sum or such a proportion in alms, to forbear such meats and drinks which the law allowed, to fast and afflict the soul (which is specified v. 13) at other times besides the day of atonement. And many similar vows might be made in an extraordinary heat of holy zeal, in humiliation for some sin committed or for the prevention of sin, in the pursuit of some mercy desired or in gratitude for some mercy received. It is of great use to make such vows as these, provided they be made in sincerity with due caution. Vows (say the Jewish doctors) are the hedge of separation, that is, a fence to religion. He that vows is here said to bind his soul with a bond. It is a vow to God, who is a spirit, and to him the soul, with all its powers, must be bound. A promise to man is a bond upon the estate, but a promise to God is a bond upon the soul. Our sacramental vows, by which we are bound to no more than what was before our duty, and which neither father nor husband can disannul, are bonds upon the soul, and by them we must feel ourselves bound out from all sin and bound up to the whole will of God. Our occasional vows concerning that which before was in our own power (Acts 5:4), when they are made, are bonds upon the soul likewise. 2. The command given is that these vows be conscientiously performed: He shall not break his word, though afterwards he may change his mind, but he shall do according to what he has said. Margin, He shall not profane his word. Vowing is an ordinance of God; if we vow in hypocrisy we profane that ordinance: it is plainly determined, Better not vow than vow and not pay, Eccl. 5:5. Be not deceived, God is not mocked. His promises to us are yea and amen, let not ours to him be yea and nay.