(21) When thou shalt vow . . . thou shalt not be slack . . .--The three yearly feasts are mentioned by Rashi and the Rabbis as occasions for the payment of vows. (See 1Samuel 1:21.) This precept is cited in Ecclesiastes 5:4, but with sufficient verbal variation to prevent its being called a quotation.

Verses 21-23. - A vow to the Lord, once made, was to be religiously kept; the Lord would require it, and to refuse or neglect to pay it would be held a sin. No one, however, was under any obligation to vow - that was to be a purely voluntary act. That which is gone out of thy lips thou shalt keep and perform... according as thou hast vowed unto the Lord thy God of free-will (נְדָבָה, spontaneously). (For the law concerning vows in general, see Leviticus 27, and Numbers 30.)

23:15-25 It is honourable to shelter and protect the weak, provided they are not wicked. Proselytes and converts to the truth, should be treated with particular tenderness, that they may have no temptation to return to the world. We cannot honour God with our substance, unless it be honestly and honourably come by. It must not only be considered what we give, but how we got it. Where the borrower gets, or hopes to get, it is just that the lender should share the gain; but to him that borrows for necessary food, pity must be showed. That which is gone out of thy lips, as a solemn and deliberate vow, must not be recalled, but thou shalt keep and perform it punctually and fully. They were allowed to pluck and eat of the corn or grapes that grew by the road side; only they must not carry any away. This law intimated what great plenty of corn and wine they should have in Canaan. It provided for the support of poor travellers, and teaches us to be kind to such, teaches us to be ready to distribute, and not to think every thing lost that is given away. Yet it forbids us to abuse the kindness of friends, or to take advantage of what is allowed. Faithfulness to their engagements should mark the people of God; and they should never encroach upon others.When thou shalt vow a vow unto the Lord thy God,.... Which must be of things in a man's power to perform, and of what are lawful to be done, and according to the mind and will of God revealed in his word, and agreeably to the manner of worship prescribed by him; as that he will offer such a sacrifice, a freewill offering to him, and the like, besides what he was bound to do, or give such and such things for the repair of the sanctuary, or for the relief of the poor; See Gill on Numbers 30:2. This law is thought by Aben Ezra to be repeated on the mention of the hire of a whore, &c. being forbidden to be brought for a vow, Deuteronomy 23:18,

thou shall not slack to pay it; or delay the payment of it, but do it immediately; since zeal and affection might abate, and there might not be hereafter an ability to perform, or death might come and prevent it; the Targum of Jonathan adds, at the three feasts, that is, of the passover, pentecost, and tabernacles; and the Jewish writers (h) say, that no man transgresses this precept respecting the delay of paying a vow, until the three feasts have passed:

for the Lord thy God will surely require it of thee; exact the payment of it, and expect it, insist upon the performance of it, and punish for neglect:

and it would be sin in thee; guilt of sin would be contracted, and punishment inflicted; Aben Ezra interprets it of the latter.

(h) Maimon. & Bartenora in Misn. Roshhashanah, c. 1. sect. 1. & in Ediot, c. 7. sect. 4.