Megillat Ta’anit is a little known collection of statements about minor holidays and fasts that commemorate events which took place during the Second Temple period. On the minor holidays, fasting and eulogies were forbidden. Most of the events that are commemorated are from the period of the Hasmonean monarchy – a prime example being the story of Hanukkah – although there are also events from earlier and later periods included, as well.
This work is set up chronologically, and it includes the date and a brief account of the incident written in Aramaic, followed by a fuller description of the event in Hebrew.
It appears that this work is the oldest example of the Oral Torah being committed to writing; the Sages of the Mishna do not only discuss the rulings that appear in it, but also the language that was used. (Although it is not part of the standard texts of Talmud, the Steinsaltz Koren Talmud Bavli includes it as an addendum to the volume that contains Massekhet Ta’anit).
The discussion in our Gemara (which begins on page 18b and continues onto our daf) revolves around the question of whether the commemorative days that appear in Megillat Ta’anit are still significant, or whether batlah Megillat Ta’anit: whether Ta’anit has become null and void.
The Gemara answers: The question whether or not Megillat Ta’anit has been nullified is the subject of a dispute between tanna’im, as it is taught in a: These days, which are written in Megillat Ta’anit, both when the Temple is standing and when the Temple is not standing, are days on which fasting is prohibited; this is the statement of Rabbi Meir. Rabbi Yosei says: When the Temple is standing, these days are prohibited for fasting because these days are a source of joy for Israel. But when the Temple is not standing, these days are permitted for fasting because these days are a source of mourning for them.
Rabbi Meir believes that Megillat Ta’anit should still be kept and Rabbi Yosei rules that it is no longer binding, since without the Temple, the days that commemorated events of the Temple are no longer applicable. In closing, the Gemara states that both positions are accepted. Megillat Ta’anit no longer applies, except for the holidays of Hanukkah and Purim.
Rav Yosef explains the uniqueness of Hanukkah as stemming from the publicity attached to the miracle, which, as Rashi clarifies, means that the mitzvot attached to the holiday had been widely accepted as obligations and they could not be done away with. The Ran points out that Purim has an even stronger basis, since the celebratory aspects of the holiday are clearly delineated in Megillat Esther, part of the written Torah.