The Halachic sources establish that “Mebatlin Torah Mipeneh Mikra Megila” – one can take time away from Torah study for the sake of the Misva of hearing the Megila reading. If one was supposed to be learning at the time of the Megila reading, he closes his books and goes to hear the Megila.
The question arises as to why hearing the Megila is considered “Bittul Torah” – taking time away from learning. After all, the Megila is part of the Tanach, and listening to the reading certainly qualifies as Torah study. Why, then, do we need to be told that one may take away time from other study to hear the Megila reading?
The Aruch Ha’shulhan (Rav Yechiel Michel Epstein of Nevarduk, 1829-1904) explains that this Halacha refers to stopping one’s learning in order to go to the synagogue to fulfill the Misva of Megila “Be’rob Am” – with a large assembly of people. If a person is learning at home, for example, he will need to take time out from his study to make it to the synagogue to hear the Megila reading, but this should nevertheless be done for the sake of attending a large, public gathering. Although he will be taking time out from learning, as he will not be learning during the time needed to get to the synagogue, this is acceptable due to the importance of a public Megila reading.
In light of this explanation, Hacham Bension Abba Shaul (Israel, 1923-1998) writes that a Torah class should be cancelled for the sake of Megila reading only if this would enable the participants to hear the Megila “Be’rob Am.” If a small group of people are learning together, and they need to interrupt in order to go to the synagogue and hear a public Megila reading, this is what they should do. However, if there is no large Megila reading in the area, and they in any event will be reading the Megila as a small group, then they should not cancel their class, and should instead read the Megila afterward.
It should be noted that this Halacha reflects the importance of reading the Megila in the synagogue, in the presence of a large group of people, which overrides even the Misva of Torah study. Unfortunately, and ironically, Purim is the time when many people make small Minyanim in their homes, rather than attend the reading in the synagogue. On Purim, Halacha clearly requires even those who normally pray in their homes to attend the synagogue to hear the Megila “Be’rob Am.” And yet, on Purim many people who normally attend the synagogue arrange Minyanim in their homes – precisely the opposite of what should happen (“Ve’nahafoch Hu…”). True, if there are extenuating circumstances that require arranging a Minyan in the home, such as if one is physically unable to go to the synagogue, or if he fears that in the synagogue he will not hear the reading properly because of the noise and commotion, a Minyan should be arranged in the home. Generally speaking, however, there is no reason not to attend the reading in the synagogue other than simple convenience, which does not justify sacrificing the special Misva of reading the Megila “Be’rob Am.”
Summary: One should attend the Megila reading in the synagogue, rather than arrange a small Minyan in his home, unless there is a valid reason not to go to the synagogue. Attending the public reading in the synagogue is so significant that Torah classes should be cancelled for the sake of the public reading.