Q. How important is it to  light a bonfire on Lag Baomer and what is the source of this tradition?
A. On question 3708 we wrote: “Sefer Ranu LeYaakov (p. 214) mentions echoing Chassam Soffer, that
the source for this very widespread tradition, is the pasuk “Eish Das
Lamo’ (Devarim 33: 2) that well describes the constant fiery fight and
combat the Rabi Shimon Bar Yochai led against those who opposed the
learning of Torah.
See also Lebush Yosef (p. 215), Ginas Reuben (p.13), Vezos LeYehuda (p.
229) and others that quote the minhag and offer other reasons. Many of
them are based on the symbolic representation of fire to the learning
and teaching of Torah, especially of the Nitzotzos or sparks of Kedusha
inherent in the Zohar and Cabalah teachings.Horav Shlomo Miller’s Shlit’a opinion is that people should maintain the traditions and minhagim of their families and congregations.Rabbi A. Bartfeld as revised by Horav Shlomo Miller, Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a