That is that He commanded us to count forty-nine days from the harvesting of the omer. And that is His, may He be exalted, saying, "you shall count for yourselves seven weeks from the morrow of the Shabbat, etc." (Leviticus 23:15). And you should know that just like the court is obligated to count the years of the Jubilee, year by year [and] cycle by cycle - as we explained in what came previously (Sefer Hamitzvot, Positive Commandments 140) - so too is each and every one of us obligated to count the days of the omer, day by day and week by week. And that is His having said, "you must count fifty days" (Leviticus 23:16), and "Seven weeks shall you count for yourself" (Deuteronomy 16:8). And just like the commandment of counting the years and the sabbatical cycles is one commandment - as we explained - so too is the counting of the omer, one commandment. And do not be fooled by their saying (Menachot 66a), "It is a commandment to count days and it is a commandment to count weeks," and think that they are two commandments. For it is a commandment to do each and every part of commandments that have have different parts. However had they said, "From where [do we know that] the days are a commandment; and from where [do we know that] the weeks are a commandment" - it would have been two commandments. And this will not be lost on the one that will not be fooled by the words. Since were you to say, "It is an obligation to do such and such," it surely does not necessarily make that action a separate commandment. And the clear proof for this is our counting every night that it is such and such weeks and such and such days. And were it to be a separate commandment, we would only arrange its content on the night of Shavuot; and we would say two blessings - on the counting of the omer; and on the counting of the weeks of the omer. But the things are not like this. Rather the commandment is counting the omer daily and weekly [together], as they ordained. And women are not obligated in this commandment. (See Parashat Emor; Mishneh Torah, Daily Offerings and Additional Offerings 10.)

And from the day on which you bring the sheaf of elevation offering—the day after the sabbath—you shall count off seven weeks. They must be complete:

You shall count off seven weeks; start to count the seven weeks when the sickle is first put to the standing grain.

§ The Gemara analyzes the matter itself of Abaye’s statement cited in the course of the previous discussion. Abaye said: It is a mitzva to count days, and it is also a mitzva to count weeks. The Gemara notes that in fact the Sages of the study hall of Rav Ashi counted days and they also counted weeks. Ameimar counted days but not weeks. In explanation of his practice, Ameimar said: Since there is no longer an omer offering, the counting is performed only in commemoration of the Temple. Therefore, one does not need to be so scrupulous to count both days and weeks.

It is a positive commandment to count seven complete weeks from the day the omer is brought, as [Leviticus 23:15] states: "And from the day after the Sabbath, you shall count... seven weeks." It is a mitzvah to count the days together with the weeks, as [ibid.:15] states: "You shall count 50 days."One should count at the inception of the [new] day. Therefore one counts at night, [beginning] from the night of the sixteenth of Nisan.

When one forgot and did not count at night, he should count during the day. One should count only when standing. If one counted while sitting, he fulfilled his obligation.

This mitzvah is incumbent on every Jewish male in every place and at all times. Women and servants are absolved from it.

Each night, the [following] blessing should be recited before counting: "Blessed are You, God, our Lord, Who sanctified us with His commandments and commanded us concerning the counting of the omer." If one counted without reciting the blessing, he fulfills his obligation and should not recite the blessing afterwards.