The Torah in Parashat Emor (23:15-16) introduces the mitzva of sefirat ha-omer – the daily counting of the forty-nine days from the 16th of Nissan – the day the special korban ha-omer sacrifice was brought in the Beit Ha-mikdash – until the festival of Shavuot.
Tosafot, in Masekhet Menachot (66a), cite the famous ruling of the Behag that if a person misses a day of counting, he no longer counts the omer thereafter. The reason for this position, as explained by Tosafot, is that the Torah requires counting “seven complete weeks” (“sheva shabbatot temimot”), and once a person misses a day of counting, he is no longer able to fulfill the requirement of a “complete” counting. Tosafot strongly reject this position, and indeed, the Shulchan Arukh (O.C. 489:8) rules that one who missed a day of counting must continue counting each night thereafter. However, in deference to the Behag’s position, the berakha over the mitzva should be omitted when one counts henceforth.
The conventional understanding of the Behag’s position is that in his view, the entire forty-nine days of counting constitute a single mitzva, such that a missed day of counting effectively denies one the possibility of fulfilling the obligation. Thus, for example, the Rosh (end of Masekhet Pesachim) cites the Ri as disputing the Behag’s ruling because “each and every night is its own mitzva” – clearly indicating that the Ri understood the Behag as viewing all forty-nine nights of counting as part of a single, integrated mitzva, and the Ri dismissed this notion.
Rav Soloveitchik, however, as cited by Rav Herschel Schachter (Eretz Ha-tzvi, pp. 17-18), suggested a different understanding of the Behag’s position. He proposed that the Behag perhaps agreed that each night of counting fundamentally constitutes an independent, separate mitzva. In practice, however, it is not possible – in the Behag’s view – to continue counting the omer after missing a day of counting, because the count must, by definition, be successive. One cannot count the thirteenth day of the omer, for example, if he had not counted the twelfth day, since there cannot be a thirteenth day without a twelfth. Thus, although in principle the mitzva to count on subsequent nights is unaffected by a missed night of counting, this is not possible as a practical matter.
The basis for this explanation of the Behag’s position is the Sefer Ha-chinukh’s comment (306) in noting the accepted practice, which, as mentioned, does not follow the Behag’s ruling. After noting the Behag’s opinion, the Sefer Ha-chinukh writes: “Our authorities in our generation did not agree to this line of reasoning; rather, one who forgot one day [of counting] counts the others with all of Israel.” Rav Soloveitchik found it significant that instead of simply stating that the individual in this case continues counting, the Sefer Ha-chinukh emphasized that the person continues counting “im kol Yisrael” – “with all of Israel.” The explanation of this remark, Rav Soloveitchik suggested, might be that the Sefer Ha-chinukh here responds to the argument that counting after a missed day cannot qualify as a proper counting since a day has been skipped. The Sefer Ha-chinukh counters that since the rest of the Jewish Nation counted the previous night, their counting suffices to allow this individual who missed the previous night to continue counting. Although he did not count the twelfth day, for example, he can nevertheless count the thirteenth day, building upon the previous night’s counting by the rest of the nation. And indeed, if it would ever occur – Heaven forbid – that all the Jews in the world miss a day of counting, then the Sefer Ha-chinukh might concede that the subsequent days cannot be counted, given the need for succession, which would not be possible in this situation. However, as long as other Jews counted the omer, one who missed a day is able – according to the Sefer Ha-chinukh – to continue counting, on the basis of the other Jews’ counting the previous day.