Ki Tavo | Arvut (Mutual Responsibility)
Moshe and the Elders commanded the nation to write the Torah on stone at Har Eival, where we were also to bring a sacrifice and rejoice before God (Devarim 27:1-8). Our parasha further cites Moshe's instructions regarding the blessings and curses declared on Har Gerizim and Har Eival. Now the Rambam established (3rd principle of Sefer Ha-mitzvot) that only eternally binding mitzvot are enumerated among the 613 mitzvot. Therefore, these commandments in our parasha, which applied only temporally, are not to be counted, just as we do not count the mitzvot charged upon Benei Yisrael at the time of Matan Torah.
The Ramban (ad loc.) attempted to explain the position of the Bahag, who did count the mitzvot concerning Har Eival but omitted from his list the mitzvot of Matan Torah. He suggested that although we were explicitly commanded to draw a boundary around Har Sinai and make various preparations to receive the Torah, those measures had no lasting effect and are therefore considered temporary obligations, which do not qualify for inclusion in the 613 mitzvot. Writing the Torah on stone, by contrast, has a lasting, permanent effect. These stones were to have remained with us forever, and the blessings and curses entail an eternally binding acceptance of Torah. Although there is no specific action that we are required to perform today, mitzvot intended to have a lasting effect are, according to the Ramban's understanding of the Bahag, counted among the 613 mitzvot.
Rabbeinu Sa'adya Gaon, too, included in his list the mitzva "to establish a covenant of the Blessings and Curses." He divided all mitzvot into three categories: mitzvot asei, mitzvot lo ta'aseh, and mitzvot which apply to the community as a whole, but entail no personal responsibility on individuals. He lists this mitzva among those which apply to the community at large.
Rav Perla explained (based on the Gemara in Sota 37b) that the specific eternal mitzva involved here is the concept of arvut. When Benei Yisrael entered Eretz Yisrael, they became one nation with mutual responsibility. When they received the Torah at Sinai, they obligated themselves merely as individuals; only once they entered the land of Israel do they become truly united into a single nation. Rav Perla found this idea so self-evident that he expresses wonder over the Rambam's omission of this mitzva. As he himself notes, however, according to this line of reasoning, this mitzva should be included in the general list of mitzvot asei, rather than in the list of communal obligations. After all, it is each person's obligation to accept mutual responsibility for every Jew.
To resolve this difficulty, let us address one basic question concerning the inherent nature of arvut: does the concept of arvut constitute a separate, individual mitzva, or should we view it as a broad, overarching principle? Perhaps the acceptance of any mitzva automatically includes an obligation of arvut with respect to that mitzva. If so, then arvut should be seen not as its own mitzva, but rather as a feature common to all 613 mitzvot. Indeed, the Gemara (Sota 37b) states quite clearly that each mitzva included 600,000 covenants, as each member of the nation bears responsibility not only for himself, but for the entire Jewish nation, as well.
One ramification of this question involves the status of women with regard to arvut. The Gemara (Berakhot 20b) discusses the issue of whether women are included in the Torah obligation of birkat ha-mazon, or obligated by force of rabbinic enactment. It explains that this question determines whether or not they can recite birkat ha-mazon on behalf of men. If the Torah exempts women from birkat ha-mazon, then they may not recite it on behalf of a man, given their lower level of obligation. The Rosh took this to mean that the concept of arvut does not apply to women. Generally, he writes, a person included in a given mitzva by force of rabbinic enactment may, in fact, perform it on behalf of someone included on the level of Torah law. Thus, for example, a man who ate but a minimal amount of food, who must recite birkat ha-mazon only mi-de-rabbanan, may nevertheless recite it on behalf of someone who ate a quantity requiring birkat ha-mazon according to Torah law. The concept of arvut means that he bears responsibility towards others, and he may therefore fulfill the obligation on others' behalf, even if his obligation applies at a lower level. Women, however, do not bear an obligation of arvut, and they may therefore not fulfill a mitzva on behalf of those with a higher level of obligation in that mitzva.
The Noda Bi-Yehuda (Dagul Me-Revava, O.C. 271) interpreted this to mean that arvut does not apply to women at all. He even raised the possibility that men might not bear the responsibility of arvut with respect to women.
Rav Akiva Eiger (Responsa, 7), however, rejected this interpretation of the Rosh. He understood the Rosh to mean that arvut does not apply regarding a mitzva in which one is not included. Only when a person is obligated in a given mitzva does he automatically become obligated in arvut concerning that particular mitzva. Therefore, if women are not biblically required to recite birkat ha-mazon, they have no obligation in arvut for that mitzva and therefore cannot fulfill the obligation on behalf of those included in the obligation. Regarding, however, those mitzvot which obligate both men and women (such as kiddush, the specific point of debate between the Noda Bi-Yehuda and Rav Akiva Eiger), arvut applies to women as much as to men.
This debate between the Noda Bi-Yehuda and Rav Akiva Eiger clearly hinges on the aforementioned question as to whether arvut constitutes an independent mitzva or is simply part of the specific mitzva involved. According to Rav Akiva Eiger, the concept of arvut exists within each mitzva, and thus everyone included in a given mitzva bears as well the obligation of arvut concerning that mitzva.
This perspective resolves the difficulty we noted with Rav Perla's approach. Generally, there is no specific mitzva of arvut, but it is rather part and parcel of each individual mitzva. If Rabbeinu Sa'adya did list an independent mitzva of arvut incumbent upon the community at large, he must refer to a special type of arvut, separate and apart from the standard obligation that applies to every individual concerning every mitzva. Rabbeinu Sa'adya here speaks of a unique obligation cast upon the community leaders to work towards ensuring the nation's compliance with the mitzvot.
Indeed, the Meiri writes (Sanhedrin 43b), "The judges, scholars and leaders must constantly check and inquire about the actions of their townspeople… since all of Israel has arvut toward each other." Evidently, in addition to the general obligation of arvut, there exists a specific obligation of arvut charged upon the leaders, and this obligation may perhaps be counted as an independent mitzva.