Shevua on a Mitzva
The gemara in Nedarim cites Rav Gidal's famous halakha that one is allowed/encouraged to take an oath to fulfill a mitzva. He bases this concept on the pasuk in Tehillim (119), "Nishbati va-akayeima li-shmor mishpetei tzidkekha" (I have sworn to fulfill mitzvot and I have performed my pledge). Despite his use of the term, "neder," Rav Gidal actually refers to a shevu'a. Typically, a neder prohibits benefit from a certain item, place or person. A shevu'a, by contrast, constitutes an oath to perform or refrain from a specific act unrelated to halakha or, in Rav Gidal's instance, to perform a mitzva. Rav Gidal's statement, though, raises questions with regard to two other gemarot - each of which appear to disqualify a shevu'a on a mitzva.
The mishna in Shevuot (27a) cites the position of Rabbi Yehuda ben Beteira enabling one to take a shevu'a on a mitzva. The mishna rules, however, otherwise, that a shevu'a can be manufactured only regarding actions which are reshut (permissible but not mandatory). The ensuing gemara derives this from the pasuk in Vayikra 5 which qualifies a shevu'a as intending to act in a desirable or undesirable fashion ("le-hara o le-heitiv"). The syntax suggests a parity between the two conditions; meaning, the pasuk includes within the realm of shevuot all actions which are optional and can equally be performed or not be performed. The existence of a mitzva clearly alters this equilibrium, and hence that realm is excluded from the halakha of shevuot.
Although this gemara seems to establish a global definition of shevu'a, seemingly disqualifying the domain of mitzvot from the world of shevua, a companion gemara in Nedarim (16b) limits the scope of this exemption. Namely, this "le-hara o le-heitiv" rule excludes an oath upon a mitzva only from the laws of korban (inadvertent violation of a shevu'a generally yields an obligation to bring a korban); it does not invalidate the shevu'a altogether. The gemara in Shevuot (27a), then, does not contradict Rav Gidal's halakha.
Yet, the same gemara in Nedarim asserts a second claim which might challenge Rav Gidal's statement. In discussing the laws of nedarim, Parashat Matot warns against violating a stated neder: "lo yachel devaro" - "he may not transgress his word." Seizing the term "devaro" – "HIS word," the gemara infers that one may not transgress HIS word, but he may transgress for Hashem's word; namely, an oath formed to violate a mitzva should be violated, rather than allow for the mitzva's violation. The gemara questions the redundancy of this inference, given that the gemara in Shavuot (27a), as we saw, invalidated a shevu'a on a mitzva based on "le-hara o le-heitiv" (Vayikra 5). The gemara answers that whereas "le-hara" excludes mitzvot from a korban, the current derasha ("devaro" as opposed to "cheftzei shamayim," Hashem's will) excludes this type of shevu'a even from the prohibition itself. Presumably, this gemara informs us that a shevu'a on a mitzva is not considered a shevu'a at all, and the 'violation' of that oath is in no way forbidden. If so, then a shevu'a on a mitzva has no halakhic validity whatsoever. The question then arises, what did Rav Gidal mean when he encouraged taking shevuot to fulfill a mitzva? If this oath has no halakhic significance at all, how does it help one ensure his compliance with that mitzva?
The Ba'al Ha-ma'or in Shevuot offers an important distinction. Unlike the 'korban' exemption of Shevuot (27), the 'lav' exemption of Nedarim is not delimiting the scope. Indeed, Shevuot (27) determines the scope of korban as encompassing only actions which are generally optional. Any oath formulated about a mitzva (to fulfill or to transgress) does not yield a korban obligation if violated. However, the gemara in Nedarim merely prescribes the protocol to follow if a neder conflicts with a mitzva. Even though normally a person should not violate his word, if to fulfill Hashem's will (a mitzva) he must violate his own oath - then so be it. Thus, a shevu'a to violate a mitzva (e.g. not to eat matza or to eat neveila) gives rise to such a conflict and should be violated. By contrast, a shevu'a to fulfill a mitzva (e.g. to lay tefillin or sit in the Sukka) creates no conflict and is therefore valid. Rav Gidal refers to precisely this case. A person is encouraged to author halakhically valid shevuot to fulfill mitzvot as a manner of creating greater incentive to fulfill a mitzva. Unlike a shevu'a to violate a mitzva, a shevu'a to fulfill one is valid. In fact, if he does not fulfill the mitzva, the valid oath has been violated and he receives malkot for its violation (and possibly a second malkot if he performed an aveira carrying the penalty of malkot).
The Ramban, in his Milchamot Hashem to Shevuot, sharply disagrees with the Ba'al Hama'or in his reading of the 'lav' exemption of Nedarim (16b), and maintains that indeed, no lav applies at all to a shevu'a on a mitzva. Thus, we cannot read the gemara as just issuing a procedure to follow when confronting a conflict between a personal shevu'a and general halakha. Rather, this gemara, like Shevuot (27a), is establishing the scope of the 'issur' of shevu'a (as opposed to the scope of the korban, which is mapped in Shevuot 27a). The statement of the gemara – "you should not violate your word but should violate your word to protect Hashem's will" in fact completely disqualifies the realm of mitzvot from shevu'a. Both a shevu'a to violate a mitzva as well as one to fulfill a mitzva are equally invalid insofar as they involve a mitzva. Obviously, according to the Ramban, the violation of a mitzva oath – even one to perform a mitzva - does not mandate malkot.
Of course, we must then ask how the Ramban reads Nedarim (8) and Rav Gidal's statement. If, indeed, any shevu'a regarding a mitzva is halakhically empty, what function does it serve according to Rav Gidal, and what was his chiddush?
This issue is somewhat difficult to determine from the Ramban's comments, and later mefarshim dispute his position. The Ketzot Ha-choshen (73:5) claims that although a shevu'a about mitzvot does not yield malkot, the actual shevu'a exists. There are three types of shevuot:
1) A classic shevu'a, which yields a korban if violated through a shogeg (inadvertently) and malkot if violated intentionally;
2) A shevu'a without korban but with a penalty of malkot;
3) A shevu'a which, though binding, carries no korban and no malkot.
It is this third category to which a shevu'a to fulfill a mitzva belongs. Rav Gidal encouraged the issuing of such shevuot - even though no penalties would apply - to lend greater motivation to the successful performance of the mitzva. By fulfilling the mitzva/shevu'a, one has avoided an issur, though no penalties have been averted.
Precedent for this type of shevu'a clearly exists – according to the Rambam. He lists two shevuot, which, though binding, carry no penalty if violated. One form is a shevu'a without mentioning Hashem's name, and the other is a shevu'a through the device known as hatfasah (literally, 'attachment' - instead of articulating a shevu'a, a person overhears someone else reciting a shevu'a and attaches himself to that process). In each of these cases, the Rambam rules that no penalty of malkot applies, despite the fact that it is prohibited to violate the shevu'a. The Ramban himself does not subscribe to the Rambam's position on these two matters, rendering these cases unacceptable as direct precedent for the Ramban's position regarding a shevu'a on a mitzva. Additionally, even accepting the Rambam's position in these two instances does not necessarily mandate the Ramban's position. In the Rambam's scenarios, the actual text of the shevu'a is incomplete or unconventional (omitting Hashem's name or merely attaching oneself to someone else's formulated oath). In the Ramban's situation, however, the actual oath is complete; it is the subject matter of the shevu'a – a mitzva - which warrants an irregular set of halakhot.
Of course, the Ketzot's impetus for this model is Rav Gidal's halakha. If this shevu'a yields absolutely no malkot AS WELL AS absolutely no issur, then what type of encouragement does Rav Gidal envision? The Afikei Yam (36:1) responds to this issue and claims that indeed, according to the Ramban no shevu'a exists in this case, just as no punishment of malkot applies. In terms of justifying Rav Gidal's statement, Tosafot (Nedarim 8a) already suggest that though no shevu'a has evolved, sufficient incentive to fulfill the mitzva/shevu'a exists in the form of avoiding the mentioning of Hashem's name in vain. Aside from neder or shevu'a concerns, a separate prohibition forbids mentioning Hashem's name in vain. In fact, according to many Rishonim, this constitutes an issur de-oraita. By employing Hashem's name through issuing a shevu'a, a person lends greater certainty that the mitzva will be performed so that the name will not be rendered in vain. Even though the shevu'a has no validity, the name of Hashem was mentioned and the individual's subsequent behavior will determine whether it was said in vain.