Thy vows are upon me, O God - The word “vow” means something promised; some obligation under which we have voluntarily brought ourselves. It differs from duty, or obligation in general, since that is the result of the divine command, while this is an obligation arising from the fact that we have “voluntarily” taken it upon ourselves. The extent of this obligation, therefore, is measured by the nature of the promise or vow which we have made; and God will hold us responsible for carrying out our vows. Such voluntary obligations or vows were allowable, as an expression of thanksgiving, or as a means of exciting to a more strict religious service, under the Mosaic dispensation Genesis 28:20; Numbers 6:2; Numbers 30:2-3; Deuteronomy 23:21; 1 Samuel 1:11; and they cannot be wrong under any dispensation. They are not of the nature of “merit,” or works of supererogation, but they are
(a) a “means” of bringing the obligations of religion to bear upon us more decidedly, and
(b) a proper expression of gratitude.
Such vows are those which all persons take upon themselves when they make a profession of religion; and when such a profession of religion is made, it should be a constant reflection on our part, that “the vows of God are upon us,” or that we have voluntarily consecrated all that we have to God. David had made such a vow
(a) in his general purpose to lead a religious life;
(b) very probably in some specific act or promise that he would devote himself to God if he would deliver him, or as an expression of his gratitude for deliverance. Compare the notes at Acts 18:18; notes at Acts 21:23-24.
I will render praises unto thee - literally, “I will recompense praises unto thee;” that is, I will “pay” what I have vowed, or I will faithfully perform my vows.