For hundreds of years, there has been a custom to light a large bonfire near R. Shimon bar Yoĥai’s grave on Mount Meron, in honor of his hilula. Ĥasidim have a custom to light bonfires in other places as well. Some light candles in their synagogues in commemoration of the hilula.

Candles and light allude to Torah and mitzvot, as it says, “For the commandment is a candle and the Torah is light” (Mishlei 6:23). Fire is a wondrous thing. Out of inanimate, cold logs and oil suddenly comes forth a flame that has tremendous power – to give light and warmth, and to burn. This is why Torah and mitzvot are compared to fire and flame. If one studies the Torah and observes the mitzvot in this dark, cold world, one gains everlasting illumination.

Ĥasidim customarily light bonfires on Lag Ba-omer to allude to the great light of the Torah’s secrets that R. Shimon bar Yoĥai revealed. The Zohar (3:291b) relates that R. Shimon bar Yoĥai revealed great secrets to his students on the day he died, which were recorded in Idra Zuta, and his students could not draw near to him because of the great fire that surrounded him.

Nevertheless, we must emphasize that the customs of rejoicing on Lag Ba-omer are not obligatory. Neither Rambam nor Shulĥan Arukh rule that one must light a bonfire on Lag Ba-omer or visit the grave of R. Shimon bar Yoĥai. Furthermore, many great Torah scholars disregard these customs altogether.