This coming Thursday will be the Fast of Estherknown in Halacha as Taanit Esther. This fast poses several questions. First, we must try to understand what is the basis for Taanit Esther. We know of Yom Kippur, which is of biblical origin, or of Taaniot at times of hardship and in commemoration of tragic events that befell the Jewish people. Taanit Estherdoes not seem to fit any of the above mentioned categories. It is clearly not from the Torah like Yom Kippur and there is no tragedy to commemorate on this day. Since Taanit Estheris an annual event, it cannot be that we are fasting due to any particular problem facing us in the present.
Another question is how can we fast on the thirteenth of Adar? We find in the Gemara (Taanit 18b) that Purim is one of the days mentioned in Megilat Taanit as days on which we may not eulogize the dead or fast. Since the halacha is that on any day we are prohibited from fasting we may not fast on the day proceeding and following it as well, how can we fast on the thirteenth which proceeds the day of Purim?
Two explanations may be found for the establishment of a fast day on the thirteenth of Adar. The Rambam in Hilchot Taaniot (Chapter 5 law 5) relates the fast to the commemoration of the fast days at the time of Esther. Though the fast at the time of Estherwas during the month of Nisan it is commemorated in Adar since in Nisan we were redeemed from Mitzrayim and the Mishkan was built it should not be a time of fasting (Beit Yosef OC 686).
Most Rishonim and Achronim find the source to Taanit Estherin the fast that accompanied the battles fought on the thirteenth of Adar at the time of Mordechai and Esther. The source for fasting at a time of war is Moshe Rabeinu who fasted and prayed at the time of the war with Amalek. This then became standard for all wars of Am Yisrael.
It would seem that the Geonim established Taanit Esthersince no explicit mention of it is found in the Gemara. Yet the Baal Hamaor as quoted by the Ran suggests that the fast is Mi’Divrei Kabala, meaning it would be part of the original format of Purim established at the time of Mordechai and Esther.
If we accept the view of Rav Zerachya Halevi (the Baal Hamaor) then we can resolve the second problem. The purpose of prohibiting fasts before or after days of rejoicing found in Megilat Taanit was to reinforce the status of these days. Since Purim was established as Divrei Kabala it is viewed as not needing any reinforcement just as the Yamim Tovim and Shabbat that originate in Torah need no reinforcement. Yet, if we take the more common view that Taanit Estheris a later addition we need to understand how can we fast on the day that proceeds Purim.
The Tur explains that we are taught in the Gemara that all days mentioned in Megilat Taanit as days of rejoicing were abolished at the time of the destruction of the Beit Hamikdash with the exception of Chanukah and Purim. This exception of Purim and Chanuka applies only to the actual rejoicing but not to the prohibition to fast before or after the day. In a similar manner the Beit Yosef explains that the Yom Tov aspect of Purim was not abolished while the Yom Tov of the proceeding day was abolished.
In the event that the Thirteenth of Adar comes out on Shabbat, as is the case this year, we fast on Thursday instead of Shabbat. Though in any other fast we would not move the fast forward but rather delay it to Sunday, on Taanit Estherwe move the fast to Thursday. Two reasons are given for moving Taanit Estherforward rather than delaying it. The first is based on a principle of Halacha that “akdumei puranita lo makdeminan” we do not bring a bad thing before its time. While other fasts are in commemoration of tragic events and therefor the principle of akdumei puranita lo makdeminan would apply to them, Taanit Esther, which does not to commemorate a tragic event, may be moved forward to Thursday. The other is pragmatic, since Sunday is Purim and we want the fast to proceed the celebration of the miracle we can not delay it and must move it forward to Thursday.
When moving the fast forward it is not moved to Friday for two reasons. First, though in the event a Taanit falls on Friday we fast on Friday, ideally we do not want to begin Shabbat in a state of fasting and hunger. Secondly, since a Taanit is meant to be a time of prayers it would be a burden in the efforts to prepare properly for Shabbat if we focused on prayers, therefore, once we are moving the fast from its intended time we move it forward two days instead of one. Let us pray, that the merit of our fast on Taanit Estherbrings redemption to the Jewish people as the fasting in the times of Estherdid.