פרשת נשא includes the laws of the נזיר or nazirite: a person who vows for a specified time to abstain from consuming grapes or grape products, cutting his hair, or touching a corpse (Num. 6:3–9). In one of her commentaries on נשא, Nehama Leibowitz raises the question, "What is the significance of the Nazirite vow in the Torah?" On the one hand, the nazirite is said to be קדש (holy) "for the entire duration of his abstinence" (Num. 6:8). On the other hand, the Torah requires the nazirite to make a sin-offering (קרבן חטאת) "on the day his period of naziriteship is completed" (Num. 6:14).
The nazirite's holiness is not hard to understand. His vows set him apart (in keeping with the literal meaning of קדש) from ordinary people; the laws of the nazirite are similar to the laws of the high priest (Lev. 21:10-12); and, as Nehama Leibowitz points out, "the Nazirite is here regarded as being on a higher spiritual plane." But "what constitutes then his sin?" To this question, Nehama Leibowitz explains, the rabbis offered different opinions.
(1) According to an anti-ascetic answer stemming from R. Eliezer Hakappar, the sin for which the nazirite had to atone was denying himself the enjoyment of wine. "If then he that merely denied himself the enjoyment of wine is dubbed a sinner," the rabbi reasoned, "all the more so does this apply to the person who denies himself the enjoyment of other pleasures of life!" Maimonides also considered the nazirite's asceticism a sin; he argued (influenced by Aristotle) that the Torah "advocates no mortification," but rather "the middle road" of eating and drinking in moderation. This interpretation seems to explain the nazirite's sin, but not his holiness: if his vows were sinful, why is he described as holy?
(2) According to a second answer, the sin did not lie in the nazirite's ascetic vows but in forsaking them. The nazirite, wrote Nahmanides, "had separated himself to be holy unto the Lord and by rights he should always continue to live a life of holiness and separation to G-d." But when "the days of his separation are fulfilled," he "returns to defile himself with worldly passions, [and] he requires atonement." This interpretation explains both the nazirite's holiness and his sin, but it raises the bar of קדושה (holiness) extremely high--probably too high for most people. Surely that can't be what the Torah intends. After all, "[this] thing is very close to you; it is in your mouth and in your heart, so that you can fulfill it" (Deuteronomy 30:14). In the same spirit, R. Ishmael b. Elisha said "it is a principle not to impose on the community a decree to which the majority of the community cannot adhere" (Hor. 3b; Av. Zar. 36a).
(3) A third answer, which is in my view the most convincing, comes from R. Solomon Astruc and R. Moses Isserles. They seem to agree with Maimonides that the Torah advocates a "middle way" of moderation. However, they see the nazirite's extreme abstinence not as a sinful departure from the middle way but as a necessary corrective for a person who was previously incapable of moderation. In the words of R. Isserles, "man must divert his evil inclinations from the extreme to the middle way. This is the basic idea of the Nazirite, when he abstains, because he observes that he has a weakness for worldly pleasures. He must go to the other extreme, in order to attain the middle way." This interpretation explains both the nazirite's sin and his holiness: the sin is his previous immoderation and inability to attain the middle way, while his holiness "will only really be in evidence, later on, after he has completed the days of his Naziriteship." This interpretation is also more in keeping with the meaning of "sin" in Hebrew (חטא), which comes from the verb להחטיא, to miss an aim or a target.
While this last answer--that of R. Astruc and R. Isserles--seems most convincing to me, I would want to amend it in two ways.
First, this answer seems too individualistic to me, in the sense that R. Astruc and R. Isserles focus exclusively on how the nazirite's vows affect him, without considering how his vows might affect others in the community. Here, I think the work of the sociologist Émile Durkheim is helpful. Durkheim argued that "the whole religious life," and indeed "society itself," suppose asceticism: "In order to serve his gods, [the believer] must forget himself" and "sacrifice his profane interests." Hence, asceticism is "a necessary school, where men form and temper themselves, and acquire the qualities of disinterestedness and endurance without which there would be no religion." Moreover, Durkheim adds, "if this result is to be obtained, it is even a good thing that the ascetic ideal be incarnated eminently in certain persons, whose speciality, so to speak, it is to represent, almost with excess, this aspect of ritual life; for they are like so many living models, inciting to effort. Such is the historic role of the great ascetics.... [T]here is something excessive in the disdain they profess for all that ordinarily impassions men. But these exaggerations are necessary to sustain among the believers a sufficient disgust for an easy life and common pleasures. It is necessary that an elite put the end too high, if the crowd is not to put it too low. It is necessary that some exaggerate, if the average is to remain at a fitting level" (my emphasis). These consequences, I would suggest, are an essential part of what makes the nazirite holy: his vows help not only him but also others to attain the middle way. Even if most ordinary people cannot and will not reach the excessively high bar set by the nazirite, his exaggerated example incites them to maintain at least a moderate level of discipline sufficient to remain within the bounds imposed by the Torah.
Second, it seems to me that these rabbis and Durkheim alike err in assuming that the only way to manage "evil inclinations" (יצר הרע) is to control, discipline, or moderate them. As I have suggested elsewhere, I think the Hasidim took a wiser view. They encouraged people not to silence or suppress their desires, but to sublimate them. Perhaps the sin of the nazirite lies in the fact that he merely moderates his desires (and incites others to do so) without elevating and redeeming those desires by connecting them to a higher purpose.