Q. Why are weddings allowed on Lag Ba’Omer but not during the rest of the Omer period?
A. The sadness of this time of year, explained as deriving from Roman times when an epidemic felled many of Rabbi Akiva’s disciples who were crucial to the war effort, is marked by not having weddings or entertainment.
There are different customs as to when the period of sadness begins and ends, but all rites allow a break on Lag Ba’Omer, the 33rd day, partly because the epidemic ceased on this day, but also because of the kabbalistic notion that a great pietist’s Yahrzeit is like a wedding (hillula): each year their soul is more firmly united with the Divine.
Lag Ba’Omer is the Yahrzeit of Rabbi Shimon bar Yochai, to whom the Zohar, the kabbalists’ great text book, is attributed by mystical tradition.