... And ye shall make proclamation on the selfsame day; there shall be a holy convocation unto you; ye shall do no manner of servile work; it is a statute for ever in all your dwellings throughout your generations.As well as in Deuteronomy 16:9–12: Seven weeks shalt thou number unto thee; from the time the sickle is first put to the standing corn shalt thou begin to number seven weeks.

While Rambam (Maimonides) suggests that the omer count obligation is still biblical, most other commentaries assume that it is of a rabbinic origin in modern times.

[3] As soon as it is definitely night (approximately thirty minutes after sundown), the one who is counting the Omer recites this blessing: Barukh atah, A-donai E-loheinu, Melekh Ha-ʿolam, asher qid'shanu b'mitzvotav v'tzivanu ʿal S'firat Ha-ʿomer.

The Sefer HaChinuch states that the Israelites were only freed from Egypt at Passover in order to receive the Torah.

The former consists of barley, which is typically an animal food, and represents the low and passive spiritual level of the Israelites immediately upon leaving Egypt; while the latter consists of wheat and represents the high and active spiritual level of the Israelites upon receiving the Torah.

[15][16][17] Historically, Karaite and Karaite-adjacent religious leaders such as Anan ben David, Benjamin Nahawandi, Muhammad ibn Isma'il, Musa of Tiflis (founder of a 9th-century Jewish movement in Babylon); and Malik al Ramli (founder of a 9th-century Jewish movement in the Land of Israel) concluded that Shavuot should fall out on a Sunday.

They are often on display in synagogues for the benefit of worshippers who count the Omer with the congregation at the conclusion of evening services.

Omer-counters come in varying forms such as: Reminders to count the Omer are also produced for tablet computers and via SMS for mobile phones.

An omer counter from the 19th century in Lancaster, Pennsylvania is preserved at the Herbert D. Katz Center for Advanced Judaic Studies.

[23]) Rabbi Yechiel Michel Epstein (author of Aruch HaShulchan) postulates that the mourning period also memorializes Jews who were murdered during the Crusades, pogroms, and blood libels that occurred in Europe.

[24] The observance of mourning customs was strengthened after the Rhineland massacres and Cossack riots which occurred in the Omer period.

[25] In modern times, the Holocaust is generally included among those events which are memorialized, in particular Yom HaShoah is observed during the Omer.

During the days of mourning, custom generally forbids haircuts, shaving, listening to instrumental music, or conducting weddings, parties, and dinners with dancing.

According to some Rishonim, it is the day on which the plague that killed Rabbi Akiva's 24,000 disciples came to an end, and for this reason the mourning period of Sefirat HaOmer concludes on Lag BaOmer in many communities.

In Kabbalah, each of the seven weeks of the Omer-counting is associated with one of the seven lower sefirot (Chesed, Gevurah, Tiferet, Netzach, Hod, Yesod, Malkuth).

The 49-day period of counting the Omer is also a conducive time to study the teaching of the Mishnah in Pirkei Avot 6:6, which enumerates the "48 ways" by which Torah is acquired.