Vows That Build Permanence
וידבר משה אל ראשי המטות כו' זה הדבר כו' ובמד' אפילו באמת אי אתה רשאי לישבע אלא אם יש בך מדות הללו כו' לכן נמסר הנדרים אל ראשי המטות
"And Moshe spoke to the heads of the tribes, etc., This is the matter, etc." (Bamidbar 30:2). And in the Midrash it is taught: even to swear truthfully you are not permitted, unless you possess these particular middos, etc. It is for this reason that the laws of nedarim (vows) were entrusted specifically to the heads of the tribes.
The Torah gives the laws of vows specifically to the tribal leaders because, as the Midrash teaches, even truthful swearing requires a person of refined character. Vows are entrusted to those with the proper middos.
דהנה נדר הוא מלשון דירה להיות חל שם שמים על דבר הנדור שעד עתה הי' דבר הרשות וע"י הנדר חל עליו מצות הנדר
For behold, the word neder (vow) is related to the term dirah (a dwelling), for through it the Name of Heaven comes to rest upon the object that is vowed; until now it was a thing of the realm of the permissible, and through the neder the mitzvah of the vow takes hold upon it.
A neder is linked to the word for 'dwelling' because vowing causes Hashem's Name to rest upon an ordinary object, transforming something permissible into something bound up with a mitzvah.
ידור נדר לה'
"He shall vow a vow to Hashem" (Bamidbar 30:3).
The verse itself frames the vow as directed toward Hashem, not as a mere personal commitment.
ומצינו נדר הראשון ביעקב אבינו והאבן הזאת כו' יהי' בית אלקים
And we find that the very first neder was made by Yaakov Avinu: "And this stone, etc., shall be a House of Hashem" (Bereishis 28:22).
The Sfas Emes points to Yaakov Avinu's vow at Beis El as the prototype of all nedarim, and notably its content was to establish a House for Hashem.
וכן בדוד המלך ע"ה אשר כו' נדר לאביר יעקב אמרו במדרש שתלה הנדר ביעקב שהוא הי' הראשון
And so too with Dovid HaMelech, peace be upon him: "who, etc., vowed to the Mighty One of Yaakov" (Tehillim 132:2). The Midrash explains that he attached the vow to Yaakov because it was Yaakov who was the first to make such a vow.
Dovid HaMelech's vow about building the Beis HaMikdash is tied back to Yaakov in the Midrash, since Yaakov originated this kind of vow.
וגם שם הנדר הי' למצוא מקום לה' משכנות לאביר יעקב
And there too the neder was to find a place for Hashem, "dwelling places for the Mighty One of Yaakov" (Tehillim 132:5).
Like Yaakov's, Dovid's vow was aimed at creating a dwelling place for Hashem in the world.
וכן איתא בגמ' הנודר כאלו בנה במה
And likewise it is stated in the Gemara: one who makes a vow, it is as though he has built a bamah (a private altar).
The Gemara compares making a vow to building a private altar, hinting at the constructive, holiness-drawing power within a neder.
ופי' רש"י בזמן איסור הבמות
And Rashi explains that this refers to the era when the bamos were forbidden.
Rashi clarifies that the comparison to a bamah refers specifically to the period when private altars were prohibited, when such an act would otherwise be improper.
אבל אלה אנשים הגדולים בנו בנין קבוע שזהו עיקר החילוק בין בית עולמים לבמה שבמה הוא באקראי
But these great men built a permanent structure; for this is the essence of the distinction between the Beis HaMikdash, the eternal House, and a bamah, since a bamah is merely something temporary and incidental.
The great tzaddikim did not build something temporary like a bamah, but a permanent edifice. The Sfas Emes draws out that the difference between the eternal Beis HaMikdash and a bamah is precisely permanence versus the incidental.
אבל אותן שיש בהם מדות הללו
But those who possess these particular middos,
He turns to describe people who possess these refined middos.
הסכמתם דבר של קיימא לעולם
their resolve establishes a thing that endures forever,
Their firm commitment brings into being something lasting and eternal rather than fleeting.
וזכו לבנין בית עולמים
and they merited the building of the eternal House.
Because of this enduring resolve, such people merited the building of the permanent, eternal House.
רמז לדבר נאמר כאן זה הדבר ונאמר בשחוטי חוץ זה הדבר
An allusion to this matter: it is stated here "This is the matter" (Bamidbar 30:2), and it is stated regarding those who slaughter offerings outside "This is the matter" (Vayikra 17:2).
A textual hint links the parsha of vows to the offerings brought outside the Mishkan through the shared phrase 'This is the matter,' connecting vows with the proper, permanent place of service to Hashem.
והעיקר שידור נדר לה' כמ"ש אם ה' לא יבנה בית שוא כו'
And the main point is that one should "vow a vow to Hashem," as it is written, "If Hashem will not build the house, in vain, etc." (Tehillim 127:1).
The central lesson is that a vow must be directed to Hashem, echoing the verse that without Hashem building the house, all human effort is in vain.
וזהו הי' מסירת הנדרים ושבועות שמסר להם מרע"ה בסוף ימיו שיוציאו בנין ביהמ"ק מכח אל הפועל:
And this was the entrusting of the nedarim and the shevuos (oaths) that Moshe Rabbeinu handed over to them at the end of his days, so that they would bring the building of the Beis HaMikdash from potential into actuality.
Moshe Rabbeinu's transmission of the laws of vows and oaths at the close of his life was meant to empower Bnei Yisrael to bring the Beis HaMikdash from potential into actual reality.
Summary: The Sfas Emes explains why the laws of nedarim were entrusted specifically to the heads of the tribes: only those with refined middos can wield the power of a vow, which draws the Name of Hashem to rest upon an otherwise permissible thing, much as the word neder is linked to dirah, a dwelling. He traces the very first vow to Yaakov Avinu, who vowed to make a House for Hashem, and shows that Dovid HaMelech's vow to build the Beis HaMikdash was tied back to Yaakov for this reason. While the Gemara compares an ordinary vow to building a temporary bamah, the great tzaddikim built something permanent, for the essence of the distinction between the eternal Beis HaMikdash and a bamah is that of the lasting versus the incidental. Those who possess these middos make their resolve endure forever and thereby merit the building of the eternal House. In handing over the laws of vows and oaths at the end of his days, Moshe Rabbeinu empowered Bnei Yisrael to bring the Beis HaMikdash from potential into actuality, for the main point is always that one vow a vow to Hashem.