Thoughtless Oaths

On the matter of oaths, God communicates a significant amount of moral doctrines to Moses in the Pentateuch.  For instance, a full 21 verses address the Nazarite vow in Numbers 6, specifying what the man or woman who takes this optional vow must abstain from although such actions are otherwise permissible, as well as how they are to restart the duration of their vow if they falter and how they are to go to the priest at the end of the devoted period.  In all vows, though, God requires that the person making the oath do so without any flippancy whatsoever.  It does not actually matter what the content of the vow is.  To casually take an oath or prematurely commit oneself when one does not realize the ramifications of such a thing is condemned:

Leviticus 5:4-5--"'"or if anyone thoughtlessly takes an oath to do anything, whether good or evil (in any matter that one might carelessly swear about) even though they are unaware of it, but then they learn of it and realize their guilt--when anyone becomes aware that they are guilty in any of these matters, they must confess in what way they have sinned."'"

The thing promised could be amoral/nonsinful or even morally good in itself, such as paying for the special care of one's elderly parents, and still, thoughtlessly vowing to do whatever it might be is immoral.  This subject is addressed in Leviticus right after the matter of accidentally or obliviously coming into physical contact with the corpses of unclean animals or human uncleanness (5:2-3) and is situated in a context of unintentional sin (4:1-31, 5:2-6, 17-19).  No dishonesty was intended, and the thing might be done exactly as promised, but dishonesty is not actually the problem in view: that would be the carelessness in a person's thoughts and words.  Care is also prescribed when Deuteronomy revisits vows, focusing on oaths in God's name or addressed to God, for Yahweh will not exempt someone from the content of an oath just because they were rash:

Deuteronomy 23:21-23--"If you make a vow to the Lord your God, do not be slow to pay it, for the Lord your God will certainly demand it of you and you will be guilty of sin.  But if you refrain from making a vow, you will not be guilty.  Whatever your lips utter you must be sure to do, because you made your vow freely to the Lord your God with your own mouth."

The only logically necessary exception, which the text does not have to mention in order for it to still have to be the case, is vowing to do something which is irrational or evil, and thus which should not be done in itself.  Since it is impossible to be obligated to do something that one has an obligation to not do, it is clear which issue supercedes the other if someone was stupid enough to vow before God to do something sinful.  Someone who promises to commit murder or some other sin, whether of lesser, equal, or greater severity, should not act on their oath since they have pledged to do something evil.  Either way, they have sinned in making an oath to do something evil or in vowing to do something and not following through, which in this case is a moral necessity.

In all situations other than this, a person sins if he or she makes a vow thoughtlessly, however good the object of that oath is--even if someone takes Nazarite vow to temporarily submit himself or herself to unnecessary restrictions to express special devotion to God (Numbers 6:1-21).  The obligation is not just to do whatever one vows as long as it is not sinful, at least to the absolute best of one's ability.  There is also an obligation to not commit oneself to anything without sincerity and genuine understanding of the thing which one is pledging oneself to, at a minimum without making assumptions or misunderstanding the issue in question.  Rather than making vows, which are obviously permitted by God's laws in the Torah but can be morally dangerous, it is safer in one sense to simply let one's yes mean yes and no mean no.