The third perek of Massekhet Megilla opens with a brief discussion of basic rules of reading the Megilla on Purim, and quickly segues to the rules and regulations that govern public Torah readings on Shabbat, holidays and during the week.
The Mishna teaches that the Megilla can be read standing or sitting, by one or more people simultaneously, and may or may not have blessings recited afterwards. The Gemara discusses how each of these rules contrasts with regular Torah readings. For example, the Torah cannot be read sitting, a rule derived from the description of the Torah taught to Moshe by God (Devarim 5:28), where Moshe is commanded to stand next to God – as if to say that God Himself was standing when the Torah was taught for the first time. Similarly, explains the Rid, in public Torah readings, due to the honor shown to the congregation and the sense that the very gathering of the congregation brings with it the presence of the Almighty, the Torah must be read while standing.
In the same vein, the Torah cannot be read by two people simultaneously. During the Torah reading in the time of the Talmud, one person read aloud and was accompanied by a meturgaman – a translator who would read the Aramaic translation – but two people could not read together, since this would make it difficult to pay attention to the reading. The baraita points to hallel and Megilla as exceptions to the rule that trei koli lo mishtama’ei – that two voices cannot be heard clearly – since they are beloved by the people who look forward to hearing them, so people pay better attention.
Two approaches are offered to explain the idea that listening closely to hallel or to the Megilla allows people to fulfill their mitzva properly. One suggestion is that someone who pays close attention will be able to discern a single voice and concentrate on it, the other argues that listening closely allows someone to listen to both voices simultaneously (as quoted by the Ran and others).