Lag B'omer is Rashbi's Day of Rejoicing; not mere rejoicing, but rather "great rejoicing." This is emphasized by the custom [to rejoice] despite the restrictions on merriment that we observe throughout the counting of the Omer. For notwithstanding the somberness of the Sefirah period … on Lag B'omer, we nevertheless reverse this conduct (in accordance with Torah), and increase in joy.
Why, we even rejoice with a groom and bride, since it is customary to hold weddings on Lag B'omer [unlike the rest of the Sefirah, when weddings are prohibited]. We will in fact be celebrating a wedding here [in 770] this Lag B'omer; not only one, but two weddings… (Lag B'omer 5759; Hisvaaduyos p. 178)
One of the causes for Lag B'omer being a day of such great rejoicing (not only in contrast with the other days of the Omer, but even compared to all other days of the year) is due to the magnitude of peace that follows divisiveness. It can be compared to light that follows darkness. (Parshas Emor 5749, fn. 40; Hisvaaduyos p. 113)
Highlight of the year
See the entry for Lag B'omer in HaYom Yom, which states that "For the Mittler Rebbe [and his Chassidim], Lag B'omer was considered one of the most outstanding festivals; we would go out [from the town] into the fields … We would eagerly await Lag B'omer an entire year!" (Ibid., in subnote)
