Deuteronomy 23:22

22.But if thou shalt forbear to vow. He confirms what he said, that they would be guilty before God who have broken their promises to Him, because no necessity compelled them to promise, and consequently that their guilt was doubled, inasmuch as they chose rather to sin when it was at their option not to vow. Thus Peter, reproving the faithlessness of Ananias and Sapphira, says, (314)

"Who hath compelled you to lie to the Holy Ghost? was not the field your own, which you might have retained? but now to defraud God of part of the price, is impious hypocrisy.”
(Acts 5:4.)

Meanwhile God indirectly inculcates sobriety in vowing, when He discharges them from it as a duty; as if He had reminded them, that there was no reason why they should incur guilt by idly promising what He does not require. And surely nothing is wiser than to be very sparing of vows; since those who run into them inconsiderately, either presently repent of them, or else pay them in a servile manner, as if it were a task to which they are driven by force, and not without annoyance and disgust, and thus destroy the grace of the act. As to the words, “that which is gone out of thy lips,” they do not refer to the ceremony, on which the Jew’s as usual too unscrupulously insist; but He puts a restraint by them on vowing, to which we are of ourselves but too much inclined. Whence it is said in Psalms 66:13,

"I will go into thy house with burnt-offerings; I will pay these my vows, which my lips have uttered, and my mouth hath spoken, when I was in trouble;"

although the Prophet intimates that in his sore straits he had always retained his composure and presence of mind, so as expressly to implore God’s help, and to manifest his constancy and confidence by making vows, still it is signified at the same time that he did not precipitately utter empty words, but spoke with serious reflection. And indeed since the tongue of many is too voluble, and goes before their heart, the main obligation of vows is not to be sought in the act of their utterance; but, to make them truly complete, a mutual agreement is required between the heart and tongue. The same expression will often occur again; and its repetition shews that it is meant to remove the scruples of the weak, lest (315) as soon as any desire to vow shall have entered their minds, they should fancy that it imposes a religious obligation. We know that among heathen nations, in the solemn dedication of their temples, a priest was appointed who should (316) first recite the words; by which ceremony they were reminded that nothing is duly offered to God except He Himself should dictate it, as it were. I allow that this reason was but little considered by them; nevertheless, by their example, God would condemn all levity, or inconsiderate fervor in sacred offerings.