Tractate Megilla primarily focuses on explaining all of the halakhot that apply to the holiday of Purim. Additionally, it devotes considerable space to the general halakhot of synagogues and Torah readings.
The primary manner in which the miracle of Purim is publicized is through the reading of the Five Megillot, and this tractate attends to the details of this mitzva. The Sages required that one read the Megilla twice, once at night and once by day. They also established additional days when the Megilla may be read, aside from the days mentioned in the Megilla itself. Similarly, the Gemara delineates how the Megilla must be read in public or by a single individual, the languages in which it may be read, who is obligated to hear the reading of the Megilla, and who may read the Megilla for the entire congregation. The tractate also enumerates the other mitzvot of the holiday that must be fulfilled specifically during the day or during the night.
Since Massekhet Megilla devotes significant attention to issues regarding the reading of the Sefer Ester, it is the only tractate that addresses the subject of a public reading of the Bible in the synagogue. Furthermore, there are four special Torah portions read on Shabbat over the course of the month of Adar, and therefore the Sages saw fit to expand on these themes and to designate this tractate as the primary source of discussion of the laws of Torah readings, as well as the sanctity of the synagogue and the sacred items therein. This includes a discussion of the days when the Torah is read publicly, a ceremony of ancient origin but one that is not mandated by Torah law. There is also a discussion of how many verses must be read, how many individuals are called to read form the Torah, and how the verses are divided among the different readers. There is a further discussion of the haftarah, the additional reading from the Prophets upon concluding the Torah reading on certain days.
Additionally, this tractate addresses a synagogue’s status and level of sanctity. Because it is a place designed for public prayer gatherings, it is considered like a mini-Temple. Consequently, comparable to the Temple, one must treat a synagogue with reverence while it is functional and even after it has been destroyed. Nonetheless, there are ways to remove the sanctity of a synagogue, either by transferring that sanctity to another item of equal or greater status, or by selling the synagogue with the agreement of the community and its representatives.