Originally, our Jewish calendar did not have a fixed number of days in each month. Each month had 29 or 30 days, depending on when witnesses spotted the new moon and reported this to the Sanhedrin (High Court). Around three hundred years after the destruction of the second Templeand the accompanying exile, Hillel II (4th century CE, Eretz Yisra’el) instituted a fixed calendar which we use until this day. The year has an average of 354 days, with the months alternating in length: Nisan has 30 days, Iyyar 29, Sivan 30, and so on. (Heshvan and Kislev sometimes have 30 and sometimes 29. These are set in such a way to prevent certain festival difficulties. For instance, according to our calendar system, Yom Kippur will never fall on Friday. We ensure these by altering the length of Heshvan and/or Kislev).
In the Torah, a date is prescribed for all of the holidays, except for one: Shavuot. The Torah (Lev. 23:15) commands us to count 49 days – seven weeks – beginning the second day of Passover. On the fiftieth day, we are to observe Shavuot. Shavuot is not connected to a date, but rather is always the fiftieth day of the Omer. Back when the months didn’t have fixed lengths, Shavuot could occur on the fifth, sixth, or seventh of Sivan. [See Source I.]
The Torah (Ex. 12) tells us that the Israelites leftEgypton the fifteenth of the first month (Nisan), and that we arrived at the Sinai desert in the third month, Sivan (Ex. 19). It does not explicitly tell us which day of the month the Israelites arrived. Furthermore, it is very surprising that the date of the giving of the Torah, which should be seen as the most momentous day in Jewish history, is not recorded in the Torah! Not only that, but the Sages in the Talmud [Source II], who often have traditions about the dates of other Biblical events, disagree about the date of the giving of the Torah: according to the Sages, it was the sixth of Sivan, and according to R. Yossi, it was the seventh! How is it possible that such an important date could be forgotten?! This is even more shocking, given that Moses cautions the people, (Deut 4:9-10) “But guard yourselves, and carefully guard your souls, lest you forget… The day upon which you stood before God at Horev…”!
If we further consult the Talmud [Source II], we find that the majority of traditions state that the Torah was not given on the fiftieth day of the Omer, but rather on the fifty-first. According to two of three Tannaitic traditions (one seen as being the Sages’, one R. Yossi’s), the Exodus was on Thursday and the giving of the Torah was on Saturday – making that the 51st day of the Omer. Only according to the third baraita, which only fits according to the Sages, the Exodus occurred on Friday, allowing the giving of the Torah to be on the 50th day of the Omer (see chart at end).
To make matters even more complicated, it has been pointed out that the halakhah today actually follows R. Yossi’s view. We have, among the practical laws of Niddah, a halakhah which is based on his opinion that three full days, not two, were required for the Israelites to separate from their spouses before the Sinaitic Revelation could occur (see Shulhan Arukh, Yoreh De`ah 196:11, and Magen Avraham to Orah Hayyim, beginning of Siman 494; see also Arukh HaShulhan 494:2, who rejects the Magen Avraham’s question).
In the writings of various later authorities, some creative solutions have been proposed for this problem. For instance, the Magen Avraham (Orah Hayyim beginning of 494) suggests that the giving of the Torah purposely was timed for the second day of Shavuot, to give some sort of Biblical source for the second day of festivals, observed only in the Diaspora. Others suggest that on Shavuot we celebrate God’s giving the Torah to Israel, not Israel’s receiving the Torah; even according to R. Yossi, God was ready to give the Torah to Israel on the Friday, the 50th day of the Omer; it was Moses’s decision which caused it to actually be given on the 51st. We celebrate the day on which God was ready to give it.
But, in truth, the Torah never tells us that the celebration of Shavuot is to coincide with the giving of the Torah. The Biblical function of this holiday has nothing to do with the Revelation. It is the day of first fruits, the day of offering a new offering (‘???? ???? ??). Perhaps the Torah purposely tried to hide the day of the Revelation so that we wouldn’t think that the Torah and its mitzvot applied on that day more than any other. Every day the Torah is supposed to be cherished by us as if it had been given that very day (see Rashi to Deut. 26:16). Perhaps this can help us in our times, when modern critical research casts doubts upon the authenticity of the Revelation account, and especially its traditional dating. The date of the Revelation is not so significant for our observance, rather, what we do with the Torah after the Revelation is the true test of our loyalty.
Furthermore, Rabbi Barukh HaLevi Epstein (1860-1941, Lithuania), in his work on prayer, Barukh She’Amar (p. 390), points out that in our tefilot we do not say “Hag HaShavuot hazeh, Yom Matan Toratenu” (“the day of the giving of our Torah”), but rather “Zeman Matan Toratenu” (“the time of the giving of our Torah”). Shavuot, the holiday of first fruits, is celebrated in the general season of the Revelation, and so in addition to Shavuot’s main themes, we commemorate the Revelation on this holiday celebrated in that season, never claiming that this in fact was the exact day upon which it happened. (So, too, on Pesah we celebrate it being “Zeman Herutenu”, “the season of our freedom” – freedom was not felt on the 15th of Nisan alone. And Sukkot is in “Zeman simhatenu”, “the season of our joy”.)
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Back in Tannaitic times, there was a disagreement among authorities as to which Torah passage should be read on Shavuot [Source III]. According to the first Tanna, we should read Deuteronomy 16, which speaks of counting seven weeks between Pesah and Shavuot, and has no mention of the Revelation. According to “Aherim”, we should read the account of the Revelation, Exodus 19. It is curious, that it is that same “Aherim” [refer back to Source I] who insists that even when the months are being set by moon sightings, every effort be made to keep the months alternating in length, 30 and 29 days, and therefore, according to him, Shavuot should only fall on the sixth of Sivan. Rav Shemaya in Source I disagrees, claiming that Shavuot can fall on the fifth, sixth or seventh. Perhaps Rav Shemaya follows in the tradition of the first Tanna of Source III; since Shavuot can fall on different days in different years, they might feel that reading a Shavuot-specific passage, rather than a Revelation passage, is more appropriate.
Digits indicate the day of the counting of the Omer.
Letters indicate the day of the month. Rosh Hodesh is in gray.