Binyamin has correctly brought up the discussion of the 'Annulment of Vows' which is indeed in this coming weeks Torah portion.
http://www.chabad.org/library/article_cdo/aid/92380/jewish/Matos.htmThe Annulment of VowsThe Torah portion Matos begins with Moshe speaking “to the tribal heads of the Jewish people, telling them that this is the word that G-d commanded.”1 The Torah then goes on to spell out the laws of vows, nedarim , and their annulment, hatoras nedarim.
In explaining why the Torah singles out the tribal heads, Rashi says that “Moshe honored the tribal heads, teaching them first.” Rashi goes on to ask, “why was this specifically mentioned here, since this was always the case? To teach us that vows can be annulled even by a single individual, if he is an expert [such as a tribal leader or other scholar].”
The following question presents itself. Since this is the section that relates to vows and not to the annulment thereof, how does Rashi deduce that the tribal leaders were singled out here to inform us that even a single expert can annul a vow — the very antithesis of making one?
The main thrust of this section is not that “If a man makes a vow to G-d, or makes an oath to prohibit upon himself, he must not break his word,”2 for that is self-understood. Moreover, this is also included in the commandment to “distance yourself from falsehood.”3
Evidently, the Torah is telling us here that notwithstanding the fact that one must keep his word, it is possible for a vow to be annulled. Thus, the main thrust of the section is to let us know that vows can be annulled in any number of ways.
This is also to be understood from the more esoteric understanding of vows and their annulment:
With regard to vows, the Yerushalmi states:4 “Does it not suffice for you that which the Torah prohibited; you seek to prohibit yourself from other matters as well!?”
The reason for this statement is obvious. G-d’s intention is that through the performance of Torah and mitzvos we transform the world into a dwelling place for Him.5 As such, spiritual service must be performed with physical entities,6 making them into vessels for G-dliness. This purpose is not served if a person removes himself from involvement with them by means of oaths and vows.
On the other hand, our Sages also state7 that “vows are a fence for abstinence,” i.e., they enable a person to perform the command to “Sanctify yourself [by refraining from indulgence] in permitted matters.”8
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