The Reading of the Megilla during the Day and at Night
The gemara in Megilla (4a) reads:
Rabbi Yehoshua ben Levi said: A person is obligated to read the Megilla at night and to read it again during the day, as the verse states (Tehillim 22:3), "My Lord, I cry by day but You do not answer, and by night but have no respite." It was similarly stated by Rabbi Chelbo in the name of Ulla of Bira: A person is obligated to read the Megilla at night and to read it again during the day, as the verse states (Tehillim 30:13), "In order that my soul may sing praises to You and not be silent; Hashem, my Lord, I will forever be grateful to You."
Tosafot and the Rambam disagree concerning the daytime reading of the Megilla. According to Tosafot (s.v. Chayav), one must recite the "She-hecheyanu" blessing over the daytime reading as well, since the main fulfillment of the requirement to publicize the miracle (pirsumei nisa) is during the day. Tosafot adduce support for their opinion from the verse quoted by Rabbi Yehoshua ben Levi, which speaks first of daytime and then of night. They further argue their point from the fact that the obligation of the Purim se'uda (meal) applies during the day, not the night. In contrast, the Rambam (Hilkhot Megilla 1:3) rules that one is not to recite the "She-hecheyanu" blessing over the daytime reading.
In order to understand this divergence of views, we will first investigate a seemingly difficult ruling recorded in the Hagahot Maimoniyot (ibid.) in the name of Rav Amram. He suggests that one who recites the Ma'ariv prayer on the eve of Purim prior to the reading of the Megilla does not insert "Al Ha-nissim." This conflicts with our standard practice of mentioning a holiday in its respective Ma'ariv. Why does Purim differ in this respect?
In explanation of the matter, Rav Joseph B. Soloveitchik zt"l distinguished between mitzvot which stem from the sanctity of the day (kedushat ha-yom), which begins at nightfall, and mitzvot which fall on a certain day, but are not a function of the sanctity of the day. The latter category may thus be applicable specifically during the day and not the night before. These would be the very mitzvot from which women are exempt according to the principle of time-bound positive mitzvot (mitzvot asei she-hazeman gerama), since they are in fact dependent on the day itself and not on the sanctity of the day. The mitzva of sukka would seem to disprove this assertion, since it is a function of the sanctity of the day, but women are nevertheless exempt. However, the gemara (Sukka 28) informs us that this exemption is due to a specific biblical verse; indeed, without this special verse which comes to exempt women, they would otherwise have been obligated.
We must qualify this principle with respect to the rabbinically mandated holidays, which involve no prohibition of melakha and therefore do not have kedushat ha-yom associated with them. This is true of Rosh Chodesh, for instance, or of Purim. The foregoing would therefore imply that the obligations of Purim are a function of the mitzvot of the day and not its sanctity. Thus, it may be said that, in fact, Purim begins during the day and the previous night is regarded as a preparation (hakhana) for it. This is implied by the terminology of the adduced verse itself: "At night I have no respite" is an expression of passivity, in contrast to the daytime when the active voice is employed - "My Lord, I call to You by day."
This, then, would be the source of Rav Amram's ruling: before the Megilla is read, no connection has been established with Purim and therefore one would not say "Al ha-nissim" during Ma'ariv. This also explains the ruling of Tosafot that one is to recite "She-hecheyanu" during the day, since the daytime reading is the primary one.
The Rambam, who disagrees with Tosafot's ruling, does not necessarily disagree with the above analysis. Rather, we can explain that his opinion is based on the technical distinction between a mitzva act (ma'aseh mitzva) and a mitzva fulfillment (kiyyum mitzva). According to this principle, when the mitzva fulfillment occurs at a later time than the mitzva act, the blessings over the mitzva are to be recited at the time of the mitzva act. For example, with respect to the mitzva of eating matza, which according to many opinions is principally fulfilled with the eating of the afikoman, we nevertheless recite the blessings over the matza when we commence to eat it earlier in the Seder. Similarly, although the primary sounding of the shofar takes place during the recitation of the Mussaf service of Rosh Ha-shana (tekiot de-me'umad), we nevertheless recite the blessings when the shofar is sounded for the first time prior to the Mussaf prayer (tekiot de-meyushav). So too with respect to Purim: since we commence the reading of the Megilla at night, we recite the appropriate blessings then (at the time of the mitzva act), and not during the day when the mitzva of reading the megilla is actually fulfilled.
The Talmud adduces two separate verses to support the halakha that mandates reading the Megilla by night and by day. According to Rav Soloveitchik, there is a great thematic difference between the two. The lesson to be derived from the verse adduced by Rabbi Yehoshua ben Levi, "My Lord, I cry by day but You do not answer, and by night and have no respite," is that of crying out to God at times of distress. Rabbi Chelbo's verse, in contrast, speaks of joyous song - "in order that my soul may sing praises to You."
These verses, in fact, capture the dual nature of Purim. In the words of Chazal, Purim is like Kippurim, a day of distress and crisis but also one of joy. This notion also supports the view that the reading of the Megilla on Purim takes the place of the recitation of the Hallel. Hallel expresses joy and praise, but also proclaims the theme of crisis: "Distress and anguish I have found, and I call out God's Name." (The Meiri even cites an opinion that if one cannot hear the Megilla, he should recite Hallel instead.)
This parallel also teaches an additional lesson. Yom Kippur is a day of national atonement for the entire Jewish people. Rav Soloveitchik in fact derived the root of tzom (fast) of Kippur from tz.m.h. or tz.m.t., which suggests an intersection or meeting of the Jewish people with each other - "For the entire people have sinned unwittingly." So, too, the Kohen Gadol would state in his Yom Kippur blessing that it should be a day of love and fellowship.
Purim, as well, is a time to express unity and kinship with our fellow Jews. Therefore, we are mandated to perform the mitzvot of sending portions of food (mishloach manot) and gifts to the poor (matanot la-evyonim). By expressing unity, we confute Haman's claim that the Jewish people is "a nation scattered and divided among the nations."
(Translated by Michael Hattin)