In the hierarchy of Jewish holidays Lag BaOmer is definitely minor. It is not mentioned in the Torah/Tanach; it has none of the limitations on work or other activities associated with Jewish festivals; and it has no impact on the daily liturgy (no Hallel, no Torah reading, no special Psalm or other text), except that Tachanun, the individual’s penitential prayer following the Amida, is omitted, as happens on days associated with simcha (joy).
The name itself reflects the apparent absence of independent content – the Hebrew letters Lamed and Gimmel = 33 in gematria. It refers to the 33rd day of the Omer period (Source #1, notes & question), which falls on 18 Iyar. In Biblical times the Omer period connected the winter barley harvest with the spring wheat harvest, and by bringing the first sheaves of each, on Passover (the second day) and Shavuot respectively, the people expressed their thanks to God for providing these food staples and permitted their consumption. These were happy moments for the people of Israel.
Rabbi Moses Sofer, the Chatam Sofer (Slovakia/Hungary, 1762-1839), brings a Midrash telling that the food the children of Israel took with them on leaving Egypt lasted for thirty days and that after three days in the desert without bread, on 18 Iyar, the man, manna, began its daily appearance (Tshuvot Yoreh Deah 233). Attribution to this early historical occasion relates Lag BaOmer to food and to the transition from one type of food to another.
The Talmud does not ascribe sadness to the Omer period nor even make reference, let alone assign special significance, to Lag BaOmer. These associations came during the Geonic times (7th – 11th centuries) when there developed a revised view of the Talmudic account of the death of Rabbi Akiva’s disciples, some 24,000 of them, during the period from Pesach to Shavuot (Source #2 & questions).
Rabbi Akiva, a key figure in the development of Rabbinic Judaism and the primary source and inspiration for Rabbi Yehuda HaNasi in his redaction of the Mishna, was the subject of controversy for his role in the Bar Kochba revolt against the Romans (132-135 CE). Much of the rabbinic leadership was hesitant about, or even opposed to, rebellion against the Romans; the revolt seven decades earlier had lead to the destruction of the Temple and further religious persecution. Bar Kochba was seen by many as arrogant and unrealistic, the leader of a band of naïve extremists. However, Rabbi Akiva was an enthusiastic supporter, citing verse for his view that Bar Kochba could be the Messiah (Source #3 & question).
The results of the revolt were disaster – Betar fell; tens of thousands of Jews, including many leading scholars, were killed; Jerusalem was systematically destroyed and a Roman city, Aelia Capitolina, built in its place. The Talmud included these events in the list of tragedies that happened on the 9th of Av (Source #4 & question) but apparently downplayed the revolt and the deaths of the Jewish warriors (“Rabbi Akiva’s 12,000 pairs of students”), with no suggestion that their deaths be commemorated for bravery or be mourned in any way.
But in the 8th and 10th centuries Natronai Gaon and Shrira Gaon (Babylonia) suggested that the deaths of Rabbi Akiva’s students had been due to shmad (Roman persecution), not to a plague, perhaps based on versions in the Talmudic texts they had. Viewing the incident now as Jewish heroism that ended tragically led to the adoption of customs of mourning. Rabbi Isaac b. Judah Ibn Ghayyat (11th century, Babylonia) mentioned the prohibition of marriage during the Sefira period – the period of counting the Omer. (Some say the marriage prohibition is an imitation of similar Roman restrictions at this time of year, but others reject that.) Rabbenu Yerucham (14th century) cited Rav Hai Gaon (died 1038, son of Rav Shrira Gaon) as prohibiting work during this period from sunset to sunrise, in memory of the death of Rabbi Akiva’s disciples.
Over the years other activities were forbidden during the Omer – haircuts in the Geonic period, in our times music and public entertainment, especially as other terrible things happened to our people in Europe at this season. (Source #5 & questions)
Lag BaOmer, a day of some simcha within the fifty day Omer period, also dates from the Geonic era. Rabbi Yaakov ben Asher (Cologne, 1270 – Toledo, Spain c. 1340), in his important Halakhic code, the Tur (Orah Hayyim 493) says “u’k’zeh horu haGeonim – thus instructed the Geonim.” Rabbi Yosef Karo in his commentary on this passage (Beit Yosef) cites various Geonim.
Rabbi Zerachiah ben Isaac Halevi Gerondi (d. 1186) may have been the first to mention Lag BaOmer, as a date when mournful Sefira restrictions are discontinued. The basis for this is a reading of the story of Rabbi Akiva’s students (included in brackets in Source #2) which says that they died from Pesach v’ad pros – until close to – Shavuot. In other words, the plague/military defeat ended sometime before Shavuot, 14 or 15 days according to Geonic interpretations.
Rabbi Menachem Ha’Meiri (13th century, Catalan) said one does not fast on Lag BaOmer, citing that as a “tradition of the Geonim” and Rabbi Jacob Moellin (the Maharil), a leading rabbi of Ashkenaz (1365-1427), listed Lag BaOmer as a mini-festival in his Sefer Minhagim. As for the number thirty-three, see Source #6.
Lag BaOmer got a big push from the Kabbalists in the 16th and 17th centuries, becoming a festival of its own, with an aura of religious ecstasy. Their tradition is that Lag BaOmer is the yahrzeit of Rabbi Shimon bar Yochai, the alleged author of the Zohar, and it is the occasion for a hillula, a festivity or “wedding between heaven and earth.” This engenders a very different set of emotions, and, indeed, customs – the rapturous gatherings on Mount Meron, where Rabbi Shimon bar Yochai is allegedly buried, bonfires, Halakah – the first haircut of very religious boys at age 3, and, of course, the study of Torah.
The celebrations at Meron became very popular amongst certain segments of the population, and generated a negative reaction from others, including Rabbi Moses Sofer of Pressburg, the Chatam Sofer. Some think that the Midrash he brought, that Lag BaOmer is the day when the manna began to fall, mentioned above, was his way of countering the Kabbalistic explanation. But this opposition did not have a major effect on Lag BaOmer’s popularity, and in Israel today, hundreds of thousands flock to Mount Meron and bonfires brighten the night sky across the country every year at Lag BaOmer.