The Torah states (Vayikra 21, 15): “And you shall count for yourselves, from the day following the Shabbat, from the day the waved Omer offering is brought, seven complete weeks shall they be.” Our Sages (Menachot 65b) had the tradition that the “day following the Shabbat” refers to the day following the first day of Pesach which is a holiday. (This is what is meant by the words, “the day following the Shabbat”, i.e. the day following the first day of Pesach which is a holiday, also known as, “Shabbaton”. Therefore, on the night following the first day of Pesach following Arvit, we immediately begin counting the Omer.) It is a Torah commandment to count the Omer beginning from the sixteenth of Nissan until the end of seven weeks, which is forty-nine days.
Nevertheless, since the Torah also states (Devarim 16, 9), “You shall count for yourselves seven weeks, from when the sickle begins to strike the stalks shall you begin to count these seven weeks”, which means from the time the Omer offering was harvested, and unfortunately nowadays the Bet HaMikdash is destroyed and we have neither the harvesting of or bringing of the Omer offering, thus, this Mitzvah of counting the Omer is only Rabbinic in nature in commemoration of the services performed in the Bet HaMikdash. Therefore, in the “Leshem Yichud” text customarily recited before counting the Omer, one should omit the phrase, “As the Torah states, ‘And you shall count for yourselves’ etc.”, for the Mitzvah of counting the Omer is no longer a Torah commandment. (Although according to the opinion of the Rambam and the Ra’avaya there is no correlation between the Mitzvah of counting the Omer and the harvesting the Omer and according to them the Mitzvah of counting the Omer is a Torah commandment even nowadays, nonetheless we do not rule this way and the Halacha in this matter follows Maran HaShulchan Aruch, whose rulings we have accepted, who has ruled that counting the Omer is only a Rabbinic commandment nowadays, for this is indeed the opinion of Rav Hai Gaon, Tosafot, Rosh, Itur, Rashba, Ran, and others.)
The Mitzvah of counting the Omer is a Mitzvah during every single day of the counting period, and for this reason we recite a blessing on it before counting every single day. However, according to the opinion of the Ba’al Halachot Gedolot, if one has forgotten to count the Omer on one day during the counting period he can no longer continue to count the Omer since it is not possible to count by skipping (for if one counts one, two, four, he has counted incorrectly; thus, if one missed counting one day he can no longer rectify this and what he counts from now on is not considered counting at all). Halachically, we hold that even if one forgot to count one day of the Omer, he may in fact continue to count the rest of the days for every day is a separate Mitzvah regardless of the other days. Nevertheless, since we always follow the great rule of “when in doubt, do not bless”, regarding the blessing we are concerned with the opinion of the Ba’al Halachot Gedolot. It comes out that if one forgot to count one day of the Omer, he should continue to count the rest of the days as usual; however, from now on he should not recite the blessing before counting.
The appropriate time for counting the Omer is at night, however, if one forgets to count at night, he may count during the day without reciting a blessing before counting, in which case he may continue counting on all subsequent nights with reciting a blessing.
Women who would like to count the Omer without reciting a blessing may do so, and this matter will be discussed further, G-d willing.
