Counting Days and Weeks of the Omer
In its description of the mitzva of sefirat ha-omer in Parashat Emor, the Torah stresses the role of the korban omer, describing the sefira as beginning "on the day in which the omer ha-tenufa (sheaf of waving) was brought." This might suggest that the mitzva of omer applies only when the Beit Hamikdash stands and a korban omer is offered. This, indeed, is the opinion of Tosafot (Menachot 66a) and several other Rishonim.
By contrast, the verses in Re'eh, which also outline the mitzva of sefirat ha-omer, make no mention of the korban omer. The Rambam indeed claims that even without a Beit Hamikdash or korban omer, the mitzva of sefirat ha-omer applies. For a more detailed discussion of this issue, see https://www.etzion.org.il/en/sefirat-ha-omer-without-beit-ha-mikdash.
The gemara in Menachot (66a) cites a dispute among the Amoraim which also appears to revolve around this issue. The gemara quotes Abaye as requiring the counting of both days and weeks during the omer. Subsequently, the gemara records that Ameimar counted days and not weeks, since he felt that the mitzva of sefirat ha-omer is performed only as a "zekher le-mikdash" (in memory of the Beit Ha-mikdash), rather than as a mitzva de-oraita. Does this gemara indicate some structural difference between the counting of days and that of weeks?
The Brisker Rav contends that in truth, no such distinction exists between the counting of days and weeks. Rather, he explains, Ameimar maintains that in the post-Temple era, the mitzva is only Rabbinic in origin. However, Chazal did not recreate the original Biblical mitzva after the destruction of the Temple. Instead, they instituted a partial counting to commemorate the destruction of the Temple. By performing this mitzva in only a partial manner, we are able to fully absorb the absence of the Mikdash.
Unlike other Mikdash-based mitzvot, sefirat ha-omer (according to this understanding of Ameimar) is completely dependent upon the Mikdash. By contrast, although the mitzva of lulav can be performed more fully in the environment of the Mikdash (seven days) than in its absence (one day), even without a Mikdash the mitzva de-oraita of lulav can, in some form, be observed. Sefirat ha-omer, on the other hand, is completely canceled after the destruction of Mikdash. To illustrate this dependence, the Sages instituted a deficient mitzvah: counting days without counting weeks. The Brisker Rav cites the Ran, who explains that for this very reason no blessing of “She-hecheyanu” is recited over this mitzva. As sefira is meant to evoke grief rather than joy, She-hecheyanu is not appropriate. To summarize, Ameimar's position does not reflect a fundamental difference between the counting of weeks and the counting of days. Instead, the entire mitzva is instituted to memorialize the Mikdash; one of its components is deleted to create this effect.
By contrast, other sources draw thematic distinctions between the two dimensions of sefirat ha-omer - the days and the weeks. For example, Rabbenu Yerucham claimed that in the absence of the Mikdash, the counting of days still applies, while the counting of weeks is no longer applicable on a de-oraita level. The only reason we continue to count weeks is to fulfill the Rabbinic requirement to continue counting as our ancestors did in the Mikdash.
Rabbenu Yerucham arrives at his position by noting that the mention of korban omer in Parashat Emor is juxtaposed to the counting of weeks, while the counting of days is stated unconditionally. Hence, the counting of days applies independently of the Mikdash, while the counting of weeks depends upon the presence of the Mikdash and the offering of the korban omer. Ameimar therefore counted days (which still applied after the churban) but not weeks, while the accepted halakha mandates counting weeks, as well, but only by force of Rabbinic enactment. Rabbenu Yerucham does not explain how these different counting experiences are structurally different from one another, and why one should be suspended after the Temple's destruction while the other remains.
The Or Sameiach develops a novel concept to explain the difference between these two series of counting. Though the festival of Shavuot proper spans only one day, its sacrifices may be offered as tashlumim ('makeup' sacrifices in the event that they were not offered during the holiday itself) for six additional days. In this respect, Shavuot resembles all other seven-day Yamim Tovim. In effect, then, Shavuot contains two different planes – an intense, single day of Yom Tov, in addition to a more encompassing, seven-day, sacrifice-based festival. Counting the DAYS of omer feeds the one-day component of Shavuot, while counting the WEEKS of omer serves as a prelude to the week-long aspect of Shavuot. In the absence of the Mikdash, the week-long component of Shavuot and the ability to bring sacrifices has receded, leaving only the one-day facet of Shavuot. Therefore, only the counting of days remains a Biblical mitzva leading up to the one-day plane of Shavuot. Counting weeks no longer applies, since the aspect of Shavuot as a week-long holiday ceases after the destruction of the Mikdash.
Interestingly, the Sefat Emet suggested a diametrically opposed view of these two counting series. While the counting of weeks is merely alluded to in Emor, it takes center stage in Re'eh, which does not even mention the counting of days. Another difference between the two parshiyot is the orientation of the omer. In Emor, the sefira succeeds the korban omer and schedules the korban shetei ha-lechem. By contrast, in Re'eh the sefira establishes the date of Chag ha-Shavuot. Hence the Emor/korban counting of days no longer applies in the absence of the Mikdash and korbanot. However, the Reeh/Shavu'ot-based counting of weeks applies – on a de-oraita level - even without a Mikdash.
By counting days and not counting weeks at all, Ameimar demonstrated this situation in dramatic fashion. Day counting was incorporated into the korbanot series and suspended after the destruction of Mikdash. The Rabbanan recreated this mitzva as a component of the Mikdash after the churban. Week counting, however, was intended only to schedule Shavuot, and was not directly affected by the absence of the Mikdash and the cessation of korbanot. However, due to a technicality (the absence of cutting the omer wheat after the churban), it can no longer be performed. As it was not a Mikdash-based practice, it never earned a Rabbinic enactment reinstating it. Hence, Ameimar counted days and not weeks.
Though they posit inverse approaches, both Rabbenu Yerucham and the Sefat Emet develop compromise positions about the status of sefira without a Mikdash. In doing so, they assign different functions to each of these counting schemes.