וידבר מֹשה אל ראשי המטות וכו’ איש כי ידר נדר וכו’ לא יחל דברו
And Moses spoke to the heads of the tribes. . . . If a man vows a vow to the Lord . . . he shall not break his word
The Ramban explains that this chapter was specifically transmitted to the heads of the tribes to indicate that, as the Sages infer (Nedarim 78a-b), they are authorized to nullify vows and oaths. The concept of invalidating vows has no basis in the Scripture (היתר נדרים פורחים באויר), hanging here only on a slender thread, so that the people should not take vows and oaths lightly. The Ramban suggests that the concept of invalidating vows was not given a clear Scriptural basis so that people would not routinely seek to nullify those vows.
To enlarge on the words of the Ramban, our master said that the Torah did not suspect that the people would take lightly the vows that they make to the Eternal. On the contrary, the Torah commanded us not to desecrate our words to the Eternal to teach us that all our words should be treated as holy – that we should take care to fulfill whatever we promise, even to a friend, that we not lie to another and that our “yes” and our “no” should be trustworthy, “כ יזה כל האדם” (for this is the whole duty of man) (Ecclesiastes 12:13).
The Scripture therefore writes “לא יחל דברו” ) (he shall not break his word), referring to our word to the Eternal that we will fulfill whatever we promise to our friend. The Sages relied on this verse for the concept of invalidating vows, because it is apparent from this verse that the reason that one may not violate his word to the Eternal is so that we would learn to fulfill whatever we promise to a friend. The Sages therefore inferred from the verse that only he may not break his word, but others may allow him to do so by nullifying his promise, because if it becomes necessary for someone to request that a sage nullify his vow, the sage will not invalidate any promises made to another person, only the prohibitions that one had imposed upon himself.
However, inasmuch as people might think that the sages were empowered to invalidate vows that are made to another person — as, indeed, our Gentile enemies say that we do to them and as Zedekiah, king of Judea, did when he commanded the Sanhedrin to annul the vow that he made to Nebuchadnezzar (Nedarim 65a), the Scripture therefore hung the invalidation of vows on a slender thread, and explained the power to invalidate, as the Ramban wrote, only by way of indirect hints. (שביבי אש)
‘זה הדבר אשר צוה ה’ איש כי ידר נדר לה
This is the matter which the Lord has commanded
Rashi comments: “זה הדבר” (this is the matter). It is a restrictive phrase intimating that the sage makes use of the term “התרה” (invalidation), while the husband (concerning his wife’s vows), uses the term “annulment” (הפרה).
This is a forced inference inasmuch as no “invalidation” of a vow is derived from a Scriptural text. Were it not for the words of the Sages, our master would have explained that the verse: “זה הדבר אשר צוה ה איש כי ידר נדר לה” (this is the word that the Lord has commanded a man when he makes a vow unto the Lord) specifies what verbal formulation a person should use in making a vow. Our master explains that our Sages relied on this verse to invent Aramaic terminology for vows, a language not understood by the ministering angels (מלאכי השרת), so that the Satan would not understand the vow and then denounce the one making the vow, for anyone who makes a vow is like one who builds an altar outside the Holy Temple (כל הנודר כאילו בונה במה).
One can explain the relation between vowing and building an altar outside the Holy Temple by reference to the saying of the Sages “גדול המצווה ועושה ממי שאינו מצווה ועושה” (one who is commanded and fulfills is greater than one who is not commanded but fulfills nevertheless). To explain this saying, the Tosafot wrote that one who is commanded has a greater desire to transgress the commandment incumbent upon him than one who is not commanded, and his evil inclination is therefore more powerful, because (Proverbs 9:17) “מים-גנובים ימתקו” (stolen waters are sweet), so that, without the assistance of the Holy One Blessed Be He, one could not withstand his evil inclination.
If so, by making himself one who is commanded, one who makes a vow incites the evil inclination within his soul. Why then should the Eternal help such a person to withstand his evil inclination, inasmuch as he subjected himself to the evil inclination. The Sages therefore properly compared one who makes a vow to one who builds an altar outside the Temple, as our master has explained at length elsewhere, and they adopted Aramaic terms for vows, so that the evil inclination would not understand the vow and then seek to entice the one making the vow into breaking his word.
This idea is hinted at by the verse “’איש כי ידר נדר לה”. The verse should be understood to be saying that if one does make a vow, one should do so in such a way that the vow will be known only to the Eternal. The Scripture therefore introduces the topic by explaining how this should be done by saying: “זה הדבר” (this is the word) as if to say that one should make a vow only with Aramaic words that are understood only by the Eternal, which means that one should use the Aramaic terms that only the Eternal — not the angels – can understand. (שביבי אש)
גדרת צאן נבנה למקננו פה וערים לטפנו
We will build sheepfolds here for our cattle, and cities for our little ones
Rashi comments: They care about their property more than about their sons and daughters, mentioning their cattle before their children. Moses told them to do the opposite: first to build cities for the children and only then folds for your flocks.
But our master interprets this verse in praise of the tribes, explaining that they did not care more for their cattle than for their children, because the dwelling places for their children were already available to them in the lands of Sihon and Og which had just been conquered? However, these dwelling places were unfortified and unprotected by security walls. If they would take up arms at the front of the army, how could they leave their wives and children behind in open cities at the mercy of the surrounding inhabitants? They therefore suggested building folds, which did not yet exist, for their cattle, and making the cities that were already there habitable by fortifying them with walls and latches.
However, Moses, our teacher, reversed their proposal for a different reason, for perhaps they would suddenly be called upon to go to battle ahead of their brothers before they had finished building the walls around their cities. How could they then leave their children in such a vulnerable condition? He therefore commanded them to build the walls for the cities first, so that they would be ready to go out into battle with their brothers. That is why Moses said: “Do what you have promised. That is why I command you to build the cities first so that you will be ready at any moment to fulfill your promise.” (שביבי אש)