L'ag BaOmer, Rashbi, and Moshiach

Mitteler Rebbe, Biurei Zohar, Parshas Balak (Free Translation)

...the thirty-three days after which a woman returns to purity [following the birth of a male child] (which is the level of L'ag BaOmer) because the first day of Pesach is [spiritually] the day of Tisha B'Av, the day on which Moshiach is born. L'ag BaOmer is the end of thirty three days of purification, etc., and then it is said "I will turn their mourning to joy" and this is the hilula of Rashbi, a spark of Moshe who is a level of Moshiach as it states "send the one whom you will send" and he [Moshe] is called the first redeemer and Moshiach is the final redeemer, as is known.