Jews celebrate a minor holiday called Lag Ba'Omer, or Counting of the Omer, celebrated this year on May 12th. Reading the history of this holiday is very enlightening and gives one a clearer perspective as to the heart of Jews who refuse to accept Yeshua as their Messiah.
Here is an excerpt from a teaching by Rabbi Pinchas Stolper
Thirty-three days following the first day of Passover, Jews celebrate a "minor" holiday called Lag Ba'Omer, the thirty third day of the Omer. It is an oasis of joy in the midst of the sad Sefirah period which is almost unnoticed by most contemporary Jews. Yet it contains historic lessons of such great severity -- that this generation must not only unravel the mystery of Lag Ba'Omer but will discover that its own fate is wrapped in the crevices of its secrets.
The seven weeks between Passover and Shavuot are the days of the "Counting of the Omer," the harvest festivities which were observed in Eretz-Israel when the Temple stood on Mt. Moriah in Jerusalem.
This fifty day period should have been a time of joyful anticipation. Having experienced the Exodus from Egypt on Pesach, every Jew literally "counts the days" from the first night of Passover until Mattan Torah - the revelation of Torah at Mt. Sinai which took place on Shavuot, exactly fifty days after the Exodus. While the Exodus marks the physical birth of the Jewish nation -- the Giving of Torah completes the process through the spiritual birth of the Jewish nation.
Each year, as we celebrate the Seder on Passover, we are commanded to "see ourselves as though each of us actually experienced the Exodus." It therefore follows that we must prepare ourselves during the Sefirah period (counting of the Omer), to once again accept the Torah on Shavuot -- to make our freedom spiritually complete.
Clearly then, the Sefirah days should have been days of joy, but instead, they are observed as a period of semi-mourning. Weddings, music and haircuts are not permitted, some do not shave during this entire period. It is on the sad side of Sefirah that we come across the holiday of Lag Ba'Omer, the one day during this sad period when our mourning is halted, when sadness is forbidden.
What is the reason for sadness during what should have been a period of joyful anticipation? The reason, the Babylonian Talmud tells us, [Yevamot:62:2] is that during this period, Rabbi Akiva's 24,000 students, who lived 1,850 years ago in the Roman dominated Land of Israel, died from a mysterious G-d sent plague. Why did they die? Because the Talmud teaches, "they did not show proper respect to one another." Lag Ba'Omer is celebrated on the thirty-third day because on that day the plague ended and Rabbi Akiva's students stopped dying. Read this interesting story here: Lag Ba'Omer
Another reference is found here: Counting Omer contemporary Jews celebrate by lighting bonfires...