Rabbi Yonasan Sacks
The Character of Ta'anis Esther
The opening Mishnah in Maseches Megillah relates the various days upon which the Megillah may be read: "The Megillah is read on the 11th, 12th, 13th, 14th, and 15th (of Adar), no earlier and no later.
Noting that the Megillah itself explicitly specifies only the 14th and 15th of Adar as appropriate times for fulfillment of the mitzvah, the Gemarah (2a) immediately seeks a scriptural source sanctioning the reading on the 11th, 12th, and 13th of Adar. The Gemarah identifies such a source: in describing the establishment of the days of Purim, the Megillah uses the plural construction of the term "bi'zmaneihem" (Esther 9), denoting a plurality of days - "z'manim harbei tiknu la'hem." This term thus implies that the Megillah may be read on days other than the 14th and 15th of Adar. The Gemarah notes, though, that the term "bi'zmaneihem" would seem to denote only two additional days. How, then, do we derive that the three preceding days may serve for the mitzvah as well?
In light of this challenge, the Gemarah reconsiders its analysis. Indeed, "bi'zmaneihem" teaches us that the 11th and 12th of Adar are fit for Megillah reading. What, then, allows for Megillah reading on the 13th ? The Gemarah answers that the fitness of the 13th is self evident and needs no source, because "Yud Gimmel Z'man Kehillah LaKol Hi." That is, the 13th day's status as a "Z'man Kehillah LaKol," a time of assembly for everyone, justifies reading the Megillah. Rashi (2a, s.v. "Z'man Kehillah LaKol Hi") explains that the 13th marks the day in history on which "everyone assembled to exact revenge from their enemies." This day thus warrants Megillah reading because the "central part of the (Purim) miracle took place" on that that day.
The Rosh (1:1), however, presents a very different possibility in the name of Rabbeinu Tam. Rather than commemorating the when the Jews of old gathered to fight, the 13th of Adar marks the day upon which "everyone gathers for the fast of Esther" - a time of assembly, not for the Jews of antiquity, but rather for Jews of the present age. This explanation presents an obvious question: why does the 13th of Adar's status as Ta'anis Esther necessarily justify the reading of the Megillah? The Gemarah's inference certainly suggests a conceptual link between the reading of the Megillah and the observance of Ta'anis Esther, but what is the nature of this connection?
To answer this question, Rav Chaim Ahron Turtzin suggests that one must understand the character of Ta'anis Esther. While fast days generally assume a tragic quality in commemorating despondent times of destruction, ample evidence suggests that, perhaps, Ta'anis Esther is quite different in this regard. For example, the Ran (Ta'anis 7a in the Rif) cites the Ra'avad who questions the permissibility of our practice of fasting on the 13th of Adar, given that Megillas Ta'anis expressly forbids the enactment of such a fast, due to Yom Nikanor . The Ra'avad adds that even though the celebrations delineated in Megillas Ta'anis are not actively observed after the destruction of the Temple, it is still forbidden to establish a public fast day on any of the listed days. The Ra'avad justifies our practice by suggesting that only fasts of suffering are forbidden on days of Megillas Ta'anis. Ta'anis Esther, however, is not a fast of suffering, and therefore does not violate the prohibition of Megillas Ta'anis. Similarly, the She'iltos (Parshas Vayakhel, 67) explains that although fast days that fall on Shabbos are generally deferred until after Shabbos ("akdumei pur'anusa lo mikadminan"), Ta'anis Esther is actually observed early (on the preceding Thursday) because it is not a tragic fast. These sources suggest that Ta'anis Esther stands unique from other fast days in being a fast day which is not colored by sadness. Why is this so?
Perhaps one can understand the unique nature of Ta'anis Esther in light of a brief comment of the Rambam at the very beginning of his Yad HaChazaka. As the Rambam concludes his "Minyan HaMitzvos HaKatzuv" in which he lists the 613 commandments, he notes that beyond the 613 biblically mandated mitzvos, Chazal innovated a multitude of rabbinic enactments. The Rambam defends the legitimacy of these enactments, namely, that they do not constitute a violation of the prohibition of "Bal Tosif," because Chazal clearly publicized that their enactments are not written in the Torah itself (see Hilchos Mamrim 2:9). In the course of this discussion, the Rambam cites an example of a legitimate rabbinic enactment: reading the Megillah on Purim. The Rambam explains that Chazal enacted the mitzvah of reading the Megillah in its time in order to proclaim the praise of Hashem and the salvation which He orchestrated, and to attest to the fact that HaKadosh Baruch Hu responds to the prayers of Klal Yisrael. In the face of adversity, we call out to HaKadosh Baruch Hu, and the salvation of Hashem comes k'heref ayin, like the blink of an eye. The Megillah is a testament to the special relationship that connects Bnei Yisrael to HaKadosh Baruch Hu. The significance of the Megillah is that HaKadosh Baruch Hu responded to our cries.
The Rambam thus suggests that the purpose of reading the Megillah is to accentuate the transition from fear and despondency to hope and joy; to emphasize that K'nesses Yisrael can find itself on the brink of disaster, and instantly find salvation. On Purim, we do not merely celebrate the miracles themselves, but rather, the metamorphosis from disaster to tranquility. The contrast is what is critical.
What emerges from the Rambam's interpretation is that the fast of Ta'anis Esther constitutes an intrinsic part of the pirsumei nisa, the publicizing and glorification of the mitzvah, itself. Ta'anis Esther sets the stage, allowing us to appreciate the direness of the situation that preceded the miracle, so that we can fully appreciate the greatness of the salvation. If so, the suggestion of the Ra'avad and the Sh'iltos that Ta'anis Esther is not a tragic fast becomes clear. The fast is not tragic, because it merely serves to compound the eventual simcha and hoda'ah on Purim itself. Moreover, Rabeinu Tam's understanding of "Z'man Kehilla La'Kol" becomes lucid as well. Our mandate to read the Megillah on the 13th is obvious, even without a scriptural source, since Ta'anis Esther does not stand as a day of sorrow independent of Purim. Rather, Ta'anis Esther is part and parcel of the pirsumei nisa which the Megillah strives to achieve. When the Jews of old gathered to fight their enemies, they gathered for "puranus." When we gather, however, we gather for pirsumei nisa.
 Megillas Ta'anis enumerates certain celebrated days that were observed during the time of the Beis HaMikdash. These days were seen almost like minor Yamim Tovim, and prohibited fasting. Yom Nikanor specifically commemorates the victory of the Chashmonaim over a Greek chieftain.