Next/This Thursday night is Lag Ba- Omer, the 33rd day of the Omer period. Since the time of the Rishonim, this has been considered a day of respite from the mourning of the Omer period; according to the most widespread custom today, it marks the end of the mourning period.
Two main reasons are brought for celebrating on Lag BaOmer. A number of Rishonim connect it to the original reason for the mourning, which is the tragic death of the students of Rabbi Akiva during this period. According to some accounts the ravage stopped on Lag BaOmer. According to other accounts there were only 33 days of the scourge scattered throughout the S'fira period, so only 33 days of mourning are called for; these are observed together from the beginning of the counting.
Many sources starting in the early Acharonim mention a tradition that this day is the yahrzeit of the Tanna Rebbe Shimon bar Yochai. While this would seem to be a sad day, it becomes a day of rejoicing because on this day he ascended to heaven to attain the reward for his righteousness, and also because on the day he passed away he transmitted many precious secrets of the Torah to his students.
However, some authors suggest original reasons, not based on known traditions, for singling out Lag BaOmer as a day of rejoicing and the cessation of mourning. Let us examine two of these.
The Benei Yissachar connects the Lag BaOmer rejoicing with the idea of the counting as a spiritual ascent from the exodus on Pesach to receiving the Torah on Shavuot. Viewing the counting as a gradual spiritual ascent is found in many ancient sources. The Zohar Chadash refers to 49 gates of impurity from which the children of Israel rose (Zohar Chadash Yitro, II:51a); the Zohar likens it to the count of days from ritual impurity to purity when a married couple can be together.
What the Benei Yissachar adds is that Lag BaOmer is a kind of critical threshold in this count; it marks a stage of progress so significant that we pass from a state of counting away from Pesach to a state of counting forwards towards Shavuot.
"When our time arrives, the time of affection in the commandment of our count towards subduing the heart [LEV] towards receiving the Torah, at the completion of counting 32 days [32 is the gematria of LEV], then is revealed the good, the hidden light which was concealed in the Torah." (Benei Yissachar on Lag BaOmer in section on Iyar.)
The Chatam Sofer [Yoreh Deah 233] suggests a number of foundations for the special status of Lag BaOmer; one is a Midrash that implies that the Jews in the desert began eating manna on this day. (The Chatam Sofer himself points out that this varies from the account in the Talmud, which says that the manna began three days earlier. Both accounts agree that the bread of Egypt gave out thirty days from the Exodus; the Midrash adds that they went three days without any bread.)
[Ed. note: This last idea would be consistent with the people going hungry and complaining about lack of food.]
What both of these explanations have in common is that Lag Baomer does not mark any special event or a division between two periods which have an inherent distinction. Rather, this day constitutes a stage in a process that by nature is gradual. Each day our insight becomes clearer, but on this day we attain a special degree of insight. Each day we reduce our dependence on our Egyptian past as the bread of Egypt is slowly exhausted from our stores and then from our bodies; on this day we stop looking to the past for our sustenance and are compelled to start looking forward towards direct dependence on Hashem.
Both approaches to Lag Baomer remind us that significant breakthroughs don't always depend on momentous events. Just as often, they can come as the result of slow and methodical progress, a little bit each day.