Aish HaTorah Yeshiva describes the spiritual significance of the upcoming festival of Lag BaOmer on their website.
Aish explains, Rabbi Akiva, the towering sage of the Mishna, exerted a powerful influence on the Torah scholars of his day, to the point that he had 24,000 disciples. Great as the members of this group was, they had one shortcoming: They failed to show proper love and respect for one another. The tragic consequence of this shortcoming was a brief but cataclysmic epidemic that claimed the lives of these students during the first 32 days of the Omer.
Aish elaborates: To get a better idea of the impact this tragedy had on the Jewish People for posterity, consider the following facts: All of the Torah that we possess and study today, with all of its interpretations, perspectives, dimensions and applications, is all the Torah of Rabbi Akiva. The Oral Torah we have today was transmitted to us by Rabbi Akiva via the five students whom he taught after the loss of his first group of disciples.
Aish then moves on to describe the meaning of Lag BaOmer: The 33rd day of the Omer signified a new period in the life of Rabbi Akiva. The last students of his aborted legacy died, and he established a new venue for his legacy. This consisted of five sages. Their names were Rabbi Meir; Rabbi Yehuda; Rabbi Elazar; Rabbi Nechemiah; and Rabbi Shimon bar Yochai. All of these names are familiar to any student of Mishna or Talmud, but the most prominent among them is the sage Rabbi Shimon, about whom we shall learn more. (There is an opinion that Rabbi Shimon later died on the 33rd of the Omer, and we therefore celebrate his memory on that day.)
If these five new students were able to survive and keep the chain going, there must have been a qualitative difference between them and their fellow disciples of Rabbi Akiva. If the first group failed in their interpersonal relationships, the second were able to rectify that defect. Just as we mourn the dimensions of Torah lost through lack of appreciation for one another, so do we celebrate the reclaimed dimensions that were made possible by devotion to one another.
Aish also addresses the association of Lag BaOmer with Rabbi Shimon Bar Yochai: As the Talmud relates (Gittin 67a) Rabbi Shimon was the member of the group who most fully internalized the lessons of his great mentor. It was he who revealed the inner depths of the Torah and unlocked the secrets of its innermost dimensions though his teachings. These teachings later served the basis for the Book of the Zohar, the primary work of Kabbalah, or hidden aspects of Torah.
Getting back to those bonfires, Aish says in conclusion, the book that systematically presents Rabbi Shimon’s teachings is called the Zohar. “Zohar” means “Glow” or “Luminescence.” Rabbi Shimon himself is referred to by the Zohar as “Botzina Kadisha,” or the “Sacred Lamp.” On Lag B'Omer, we honor his memory by lighting candles or bonfires, symbolic of the light provided by the eternal fire of the Torah, particularly its inner dimensions which were revealed by Rabbi Shimon.