Even though the joy over the salvation was great, it was initially unclear how the event should be marked. Esther wrote to the Sages, “Write an account of me for future generations,” that is, write down the Purim story and include it as one of the holy books of the Tanakh. Esther further requested, “Establish me for future generations,” that is, establish the days of Purim for future generations as days of joy and reading the Megilla. At first, the Sages were unsure about this, both because it might arouse feelings of vengefulness among the nations of the world to see Israel rejoicing over their downfall, and also because they were uncertain whether it was appropriate to add to the Torah another description of Israel’s war against Amalek. In the end, they found scriptural allusions indicating that there are grounds to write about the battle of Amalek once again. Thus, the Men of the Great Assembly composed Megilat Esther (the Scroll of Esther) through divine inspiration and established Purim as a holiday for future generations (Megilla 2a, 7a; bb 15a).
The Men of the Great Assembly (Anshei Knesset Ha-gedola) constituted the supreme beit din that functioned at the beginning of the Second Temple period. It was comprised of 120 elders, among them prophets and sages such as Ĥagai, Zekharia, Malakhi, Daniel, Ĥanania, Mishael, Azaria, Ezra the Scribe, Neĥemia b. Ĥakhalia, Mordechai (the same Mordechai that appears in Megilat Esther), and Zerubavel b. She’altiel. Ezra the Scribe was the most prominent of all, so much so that the Men of the Great Assembly are sometimes called “The Beit Din of Ezra the Scribe.” They were the great beit din that established the first major enactments that are considered rabbinic mitzvot, and they were the impetus for the continued activity of the Sages of the Oral Torah.
The Purim miracle is considered the last miracle that was allowed to be recorded in the Tanakh, as the Sages state, “Esther is the end of all the miracles” (Yoma 29a). Thus, in effect, the writing of Megilat Esther concludes the Tanakh.
Purim is the link that connects the Written Torah and the Oral Torah. This is reflected in the status of its mitzvot, which are considered divrei kabbala, an intermediate category between Torah commandments and rabbinic ones. On the one hand, they are not on the level of mitzvot that are written in the Pentateuch. On the other hand, they are not considered rabbinic mitzvot, since Megilat Esther is included in Scripture. The Rishonim disagree about how one should behave if an uncertainty arises regarding the laws of Purim: Does the halakha demand that one be stringent, as in cases of Torah commandments, or lenient, as in cases of rabbinic enactments?
One must perform seven mitzvot on Purim. Four of them are unique to Purim: 1) reading the Megilla; 2) mishlo’aĥ manot (sending gifts of food to a friend); 3) matanot la-evyonim (giving gifts to the poor); and 4) participating in a festive meal. The remaining three are rabbinic commandments that parallel rabbinic obligations on other holidays: 1) reading the Torah (for men); 2) commemorating the day by reciting Al Ha-nisim in our prayers and in Birkat Ha-mazon; and 3) refraining from fasting and delivering eulogies.