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 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 F8 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.
F8 Maimon. & Bartenora in Misn. Roshhashanah, c. 1. sect. 1. & in Ediot, c. 7. sect. 4.