The Shulchan Aruch rules that in a situation where there is no Minyan for the reading of the Megilla, each person should read the Megilla individually. (Of course, if someone does not know how to read the Megilla properly, he may have someone read it for him.) The Magen Avraham comments that one can infer from the aforementioned ruling of the Shulchan Aruch that an individual should preferably not read the Megilla to discharge another person’s obligation unless there is a Minyan present. This is unlike Shofar, where we permit one individual to blow Shofar for another, even when the second individual is able to blow for himself. The Magen Avraham explains that the reason for this distinction is that the reading of the Megilla is like Tefilla, “Dilo Dami Lishofar Dikriat Hamegilla Havey Kimin Tefilla Uviinyun Asara.”
Rav Soloveitchik offers the following interpretation of the Magen Avraham’s comparison of Kriat Hamegilla to Tefilla. The Gemara in Masechet Megilla 14a states that there is no obligation to say Hallel on Purim due to the fact that “Kriata Zu Halaila,” “its reading is like Hallel.” The reading of the Megilla is a Hallel in and of itself. Regarding Hallel itself, the Magen Avraham writes that one should not be Motzi another individual who is able to read Hallel on his own, because Hallel is similar to Tefilla. The Rav, therefore, explains that according to the Magen Avraham, since Kriat Hamegilla is comparable to Hallel, it takes on the status of Tefilla and one should only be Motzi others in the presence of a Minyan.
The comparisons between Kriat Hamegilla and Tefilla can be further understood based on the Gemara in Masechet Megilla 4a. The Gemara states in the name of R’ Yehoshua ben Levi that one is obligated to read the Megilla at night and then to repeat it during the daytime as it states in Tehillim 22:3, “ Elokei Ekra Yomam Vilo Taane Vilaila Vilo Dumya Li,” “O my God, I call out by day, but you do not answer, and by night, but there is no respite for me.” The Gemara later reiterates the Halacha but this time in the name of R’ Chelbo and with the Pasuk, “ Limaan Yizamercha Kivod Vilo Yidom Hashem Elokai Liolam Odeka,” “So that my soul might sing to you and not be stilled, Hashem, my God, I will forever thank you.”
Why do the Amoraim dispute the source of the same Halacha? In truth, both R’ Chelbo and R’ Yehoshua ben Levi believe that there is a fulfillment of Tefilla when one reads the Megilla; they disagree, however, as to the nature of Tefilla. R’ Chelbo understands that Kriat Hamegilla assumes an expression of Tefilla most similar to a Hallel (“Limaan Yizamercha…”), whereas R’ Yehoshua ben Levi, on the other hand, understands that Kriat Hamegilla represents a cry for assistance from Hashem. (This is alluded to in Rashi (Dibur Hamatchil “Vilishnota Hayom”) where he states that the reason we repeat the Megilla during the day is to remind us of the miracle of Purim when we cried out to Hashem day an d night for assistance.) Regardless of the approach, further support for the link between Megilla and Tefilla can be demonstrated from the practice to read Megilla twice. The Gemara states (Berachot 32b) that if a person sees that he has prayed and has not been answered, he should pray again. We too, then, repeat the Megilla as a form of Tefilla to Hashem in our hope that just as Hashem answered our prayers in those days, He should answer us in our time as well.