On the first night of Shavuot, the Rebbe Rashab
of Chabad would pray the Evening Prayer at great length, the same as he would on
the first night of Rosh Hashanah, and with a similar extra measure of devotion.
However, unlike Rosh Hashanah, he did so privately in his room, so very few
people were aware of it...
His [Reshab’s] son and successor, the Rebbe Rayatz
used to say that every year on Shavuot, the same Divine revelation that took
place at Mt Sinai is repeated again, and even if we can’t perceive it, any Jew
who arouses within himself the commitment to establish set times for daily Torah
study is guaranteed that he will have success.
He also used to say that on the first night of
Shavuot, every Jew should accept upon himself the "yoke" of Torah with his full
heart. He should actually express this commitment in words, saying, "Ribono
Shel Olam – Master of the Universe, I accept upon myself unconditionally the
yoke of Torah."
His [Reyatz’s] son-in-law and successor, the Lubavitcher
Rebbe of our generation, taught that it was the custom of all his
predecessors as Rebbe to say words of Torah from the Baal Shem Tov and a
story about him at the Shavuot Festival meal, and that it is appropriate for
everyone follow this custom, in honor of the Baal Shem Tov's yahrtzeit on
the first day of Shavuot.
[Based on Lma'an Yishme'u-Shavuot]