The mitzva of sefirat ha-omer (counting the omer) is mentioned in the Torah in two places. In Parashat Emor we read:
And you shall count for yourselves from the morrow after the sabbath, from the day that you brought the omer of the wave offering; seven complete sabbaths shall there be: to the morrow after the seventh sabbath shall you count fifty days, and you shall bring a new meal offering to the Lord. (Vayikra 23:15-16)
In Parashat Re’eh we find:
Seven weeks shall you count; from such time as you begin to put the sickle to the corn shall you commence to count seven weeks. And you shall keep the feast of weeks… (Devarim 16:9-10)
The main talmudic discussion of this mitzva is found in Menachot 65-66. The Gemara there brings a dispute between Abaye and Ameimar whether one must count both the days and the weeks:
Abaye said: The mitzva is to count the days and also to count the weeks. The Rabbis of the school of Rav Ashi used to count the days as well as the weeks.
Ameimar used to count the days but not the weeks, saying: It is only a reminder of the Temple. (Menachot 66a)
In the Rishonim we find three different understandings of the dispute. According to one opinion, the entire discussion relates to Torah law. That is to say, Abbayei and Ameimar disagree as to what the Torah commands, with Ameimar arguing that even Torah law distinguishes between days and weeks.
A second position maintains that the entire discussion relates to the Rabbinic level. That is to say, Abaye and Ameimar disagree about what exactly the Sages instituted as a reminder of the Temple, and what exactly is meant by a reminder of the Temple. “A reminder of the Temple” can be understood to mean a commemoration of the destruction of the Temple, as proposed by the Ba’al Ha-Ma’or. If so, there is room to understand that the Rabbis only instituted part of the mitzvafor future generations, and therefore Ameimar maintains that we count only the weeks. Abaye, on the other hand, can maintain one of the two following positions. He might understand that “a reminder of the Temple” means a reminder of the Temple when it was standing, as is the case with respect to the various enactments of Rabban Yochanan ben Zakkai, and therefore the mitzva for all generations is to count both weeks and days.
A second possibility is that Abaye agrees with Ameimar that a reminder of the Temple means a reminder of the destruction, but he sees no reason to distinguish between the obligation to count the weeks and the obligation to count the days. Accordingly, the Sages enacted that the mitzvabe performed just as it had been performed in the Mikdash.
This shiur, however,will focus on a third position, that of Rabbeinu Yerucham. Rabbeinu Yerucham (5:4) maintains that these two aspects constitute fulfillment of two separate mitzvot. One mitzva relates to the omer offering from which the counting begins, and this is the mitzva to count the weeks. A second mitzva connects Pesach to Shavuot, and this is the mitzva to count the days. Rabbeinu Yerucham argues that it follows from this that two separate blessings should be recited over these two different mitzvot. This was all true during the period that the Temple stood, but today, when there is no Mikdash, and therefore there is no omer offering, what is left is only the mitzva to count the days, and only upon that is a blessing recited.
The Rambam, in his Sefer Ha-mitzvot (asei 161), raises this notion as a possibility: