All Biblical Jewish holidays but one are distinguished by specific mitzvot, or commandments, that attend their celebration: Rosh Hashana's shofar, Yom Kippur's fasting, Sukkot's booths and "four species," Passover's seder and matzah.
The one conspicuous exception is Shavuot, which falls this year on May 19 and 20. Although the standard prohibitions of labor that apply to the other holidays apply no less to Shavuot, and while special sacrifices were brought in Temple times on every Jewish holiday, there is no specific ritual or "objet d'mitzva" associated with Shavuot.
There are, of course, foods traditionally eaten on the day – specifically dairy delectables like blintzes and cheesecake. And there is a widely-observed custom of spending the entire first night of Shavuot immersed in Torah readings and study. But still, there is no Shavuot equivalent to the shofar or the etrog or the seder.
The early 19th century Chassidic master Rabbi Levi Yitzchok of Berditchev suggested that perhaps the mitzvahlessness of Shavuot is the reason it is referred to throughout the Talmud as "Atzeret" – which means "holding back" and refers to the prohibition of labor. The fact that Shavuot is essentially characterized by "not doing" rather than by some particular mitzvah-act, though, may say something deeper.
Shavuot, although characterized by the Torah only as an agricultural celebration, is identified by the Jewish religious tradition with the day on which the Torah was given to our ancestors at Mount Sinai.
That experience involved no particular action; it was, in a sense, the very essence of passivity, the acceptance of G-d's Torah and His will. That revelation was initiated by G-d; all that our ancestors had to do – though it was a monumental choice indeed – was to receive, to submit to the Creator and embrace what He was bestowing on them.
Indeed, the Midrash compares the revelation at Sinai to a wedding, with G-d the groom and His people the bride. (Many Jewish wedding customs even have their source in that metaphor: the canopy, according to sources, recalls the tradition that has the mountain held over the Jews' heads; the candles, the lightning; the breaking of the glass, the breaking of the tablets of the Law.)
And just as a marriage is legally effected in the Jewish tradition by the bride's simple choice to accept the wedding ring or other gift the groom offers, so did the Jewish people at Mount Sinai create its eternal bond with the Creator by accepting His gift of gifts to them.
That acceptance may well be Shavuot's essential aspect. A positive, active mitzvah for the day – an action or observance – would by definition be in dissonance with the day's central theme of receptivity.
And so the order of the day is to reenact our ancestors' acceptance of the Torah – pointedly not through any specific ritual but rather by re-receiving and absorbing it. Which is precisely what we do on Shavuot: open ourselves to the laws, lore and concepts of G-d's Torah, our Torah – and accept them anew, throughout the night, even as our bodies demand that we stop and sleep.
The association of Shavuot with our collective identity as a symbolic bride accepting a divine "marriage gift," moreover, may well have something to do with the fact that the holiday's hero is... a heroine: Ruth (whose book is read in the synagogue on Shavuot); and with the fact that her story not only concerns her own wholehearted acceptance of the Torah but culminates in her own marriage.
It is unfashionable these days – indeed it violates the prevailing conception of cultural correctness – to celebrate passivity or submission, even in those words' most basic and positive senses.
But it might well be precisely what we Jews are doing on Shavuot.