ט֖וֹב אֲשֶׁ֣ר לֹֽא־תִדֹּ֑ר מִשֶׁתִּדּ֖וֹר וְלֹ֥א תְשַׁלֵּֽם׃
Mejor es que no prometas, que no que prometas y no pagues.
Kedushat Levi
The words לא יחל דברו ככל היוצא מפיו יעשה, may also be the basis of a halachic ruling concerning the care to be taken when uttering a vow, even when one fully intends to keep it. The Talmud Nedarim 10 illustrates this when discussing the line ימיו כצל עובר, “man’s days (lifetime) pass as speedily as a passing shadow.” According to the Talmud there, it is forbidden to use the formula לה' קרבן,"”, “for the Lord a sacrificial offering,” the reason being that one may die a sudden death before completing the word קרבן, in which case one would have concluded one’s life by uttering the name of the Lord in vain. The appropriate formula therefore is: קרבן לה', “a sacrificial offering for the Lord.” This is what the Midrash alludes to when commenting on the words איש כי ידור נדר לה', i.e. when formulating a vow the word לה' should be the last word in the formula. [The Midrash quoted was inspired by the words “one must carry out what one has promised” being superfluous, as the Torah already warned us not to profane our word (of honour), Ed.]
We find a discussion in Nedarim 9 where Rabbi Meir interprets the advice of Solomon in Kohelet 5,4 טוב שלא תדור משתדר ואינו משלם, as meaning: “it is better not to make a vow to donate something to the Temple or to charity, than to make such a vow and then fail to honour it.” Rabbi Yehudah, on the other hand, understands the saying differently, i.e. Solomon making a comparison between two less than ideal situations, but that Solomon would agree that the best way to insure that one pays a promise, is to reinforce it by a vow and to keep the vow. It is possible to understand Rabbi Meir as referring to the formulation of the vow, i.e. to make sure, as the Torah does, that the word לה' is at the end of the formulation to avoid possibly uttering the name of the Lord in vain, in case one died suddenly. According to the view of the Torah as expressed in our verse, it is best to avoid making promises which involve invoking the name of the Lord.
We find a discussion in Nedarim 9 where Rabbi Meir interprets the advice of Solomon in Kohelet 5,4 טוב שלא תדור משתדר ואינו משלם, as meaning: “it is better not to make a vow to donate something to the Temple or to charity, than to make such a vow and then fail to honour it.” Rabbi Yehudah, on the other hand, understands the saying differently, i.e. Solomon making a comparison between two less than ideal situations, but that Solomon would agree that the best way to insure that one pays a promise, is to reinforce it by a vow and to keep the vow. It is possible to understand Rabbi Meir as referring to the formulation of the vow, i.e. to make sure, as the Torah does, that the word לה' is at the end of the formulation to avoid possibly uttering the name of the Lord in vain, in case one died suddenly. According to the view of the Torah as expressed in our verse, it is best to avoid making promises which involve invoking the name of the Lord.