Lag B'Omer, is a Jewish holiday celebrated on the 33rd day of the Counting of the Omer, which occurs on the 18th day of the Hebrew month of Iyar.
This day marks the celebration of Rabbi Shimon bar Yochai, a Mishnaic sage and leading disciple of Rabbi Akiva, and the day on which he revealed the deepest secrets of kabbalah in the form of the Zohar (Book of Splendor), a landmark text of Jewish mysticism.
This association has spawned several well-known customs and practices on Lag B'Omer, including the lighting of bonfires, pilgrimages to the tomb of Bar Yochai in the northern Israeli town of Meron, and various customs at the tomb itself.
Another reason for why Jews celebrate Lag BaOmer is that it marks the day that the plague that killed Rabbi Akiva's 24,000 disciples came to an end.
The most well-known custom of Lag BaOmer is the lighting of bonfires throughout Israel and worldwide wherever religious Jews can be found. In Meron, the burial place of Rabbi Shimon bar Yochai and his son, Rabbi Eleazar, hundreds of thousands of Jews gather throughout the night and day to celebrate with bonfires, torches, song and feasting. This was a specific request by Rabbi Shimon bar Yochai of his students. Some say that as bar Yochai gave spiritual light to the world with the revelation of the Zohar, bonfires are lit to symbolize the impact of his teachings. As his passing left such a "light" behind, many candles and/or bonfires are lit.
The Bnei Yissaschar cites another reason for the lighting of bonfires. On the day of his death, Rabbi Shimon Bar Yochai said, "Now it is my desire to reveal secrets... The day will not go to its place like any other, for this entire day stands within my domain..." Daylight was miraculously extended until Rabbi Shimon had completed his final teaching and died. This symbolized that all light is subservient to spiritual light, and particularly to the primeval light contained within the mystical teachings of the Torah. As such, the custom of lighting fires symbolizes this revelation of powerful light.
For Zionists, the bonfires are said to represent the signal fires that the Bar Kokhba rebels lit on the mountaintops to relay messages, or are in remembrance of the Bar Kochba revolt against the Romans, who had forbidden the kindling of fires that signalled the start of Jewish holidays.
It is customary at the Meron celebrations, dating from the time of Rabbi Isaac Luria, that three-year-old boys be given their first haircuts, while their parents distribute wine and sweets. Similar celebrations are simultaneously held in Jerusalem at the grave of Shimon Hatzaddik for Jerusalemites who cannot travel to Meron.
In modern Israel, early Zionists redefined Lag B'Omer from a rabbinic-oriented celebration to a commemoration of the Bar Kokhba revolt against the Roman Empire (132–136 CE). According to work published by Yael Zerubavel of Rutgers University, a number of Lag B'Omer traditions were reinterpreted by Zionist ideologues to focus on the victory of the Bar Kokhba rebels rather than their ultimate defeat at Betar three years later.
The plague that decimated Rabbi Akiva's 24,000 disciples was explained as a veiled reference to the revolt; the 33rd day when the plague ended was explained as the day of Bar Kokhba's victory. By the late 1940s, Israeli textbooks for schoolchildren painted Bar Kokhba as the hero while Rabbi Shimon bar Yochai and Rabbi Akiva stood on the sidelines, cheering him on. This interpretation lent itself to singing and dancing around bonfires by night to celebrate Bar Kokhba's victory, and playing with bows and arrows by day to remember the actions of Bar Kokhba's rebel forces.
Today, Lag BaOmer is "a symbol for the fighting Jewish spirit". The Palmach division of the Haganah was established on Lag BaOmer 1941, and the government order creating the Israel Defense Forces was issued on Lag BaOmer 1948.