The custom of all Jewry, since the geonic period, is to fast on the thirteenth of Adar in commemoration of the fasts that Esther observed before approaching King Aĥashverosh to annul the decree against the Jewish people (Esther 4:16) and the fast that the Jews observed on the thirteenth of Adar of that year. The wicked Haman decreed that on the thirteenth of Adar, all Jews – young and old, children and women – be destroyed, massacred, and exterminated on a single day, and that their possessions be plundered. Because of the miracle of Purim, the hanging of Haman, and the rise of Mordechai and Esther, King Aĥashverosh issued a second letter allowing the Jews to defend themselves and kill their enemies on that same day. The original decree, however, was not rescinded, because a decree that was written and signed by the king could not be annulled. Therefore, the enemies of Israel also had permission to kill the Jews. In other words, the kingdom established the thirteenth of Adar as the day on which those who hated the Jewish people were permitted to kill them, but the Jews were also permitted to fight for their lives and kill their enemies as well. And even though Mordechai was already second in command to the king, the Jews were still in grave danger and in need of divine mercy to help them overcome and kill their enemies. Therefore, the Jews who could not fight stirred themselves to repentance and fasted that day, as is Israel’s practice in times of hardship. Indeed, there is no greater penitence than penitence that is achieved through fasting, as fasting purifies a person’s material side and returns his spirituality to its natural, central place.
In commemoration of that fast, the Jewish people fast on the thirteenth of Adar every year. We still have enemies who want to destroy us and we still need to fast and repent every year anew.
In general, the laws of Ta’anit Esther (the Fast of Esther) are more lenient than those of the other minor fasts, because the other fasts were instituted by the Sages, whereas Ta’anit Esther was established by Jewish custom. In practice, though, there is almost no difference between them.
The laws regarding the prayers and Torah reading at Shaĥarit and Minĥa on Ta’anit Esther are the same as on all the minor fasts. The only difference is that we omit Taĥanun at Minĥa, since it is the day before Purim (mb 131:33). In addition, those who follow Ashkenazic custom and usually recite Avinu Malkeinu on fast days at both Shaĥarit and Minĥa do not do so at Minĥa on Ta’anit Esther. When the thirteenth of Adar coincides with Shabbat, we fast on the Thursday prior, and since the fast is not on the eve of Purim, we pray Minĥa as on all other fasts.
. Since Ta’anit Esther is based on custom, we are more lenient in cases of uncertainty. Thus, a woman is exempt from fasting on Ta’anit Esther for 24 months after giving birth. Even though the poskim dispute this law when it comes to the other minor fasts – most of them taking a more stringent approach, as explained above, 7:8 – there is room to rule leniently regarding Ta’anit Esther.
A bride and groom during the seven-day period of joy after their wedding, as well as the main participants in a brit mila, must observe the other minor fasts but are exempt from fasting on Ta’anit Esther. This is stated in sht 686:16, Kaf Ha-ĥayim 686:16, 28, and Yeĥaveh Da’at 2:78. (According to the Vilna Gaon, they are exempt from all the minor fasts.) Rema 686:2 maintains that the main participants in a brit must fast on Ta’anit Esther, and many follow this ruling. With regard to a bride and groom, however, it is customary to be lenient.
Rema 686:2 states that those who have severe eye pain need not fast on Ta’anit Esther, but they should make up the fast on a different day. Most Aĥaronim explain that even though those who suffer from eye pain are not considered truly sick, they may postpone their fast to a different day because they are in pain. This is not the case regarding the other minor fasts, on which one must fast even if he is in pain. In practice, it is difficult to distinguish between illness and pain. Mikra’ei Kodesh (Harari) ch. 3 n. 25 rules similarly, quoting R. Shaul Yisraeli and R. Mordechai Eliyahu, that those who suffer from eye pain have the same status as a sick person: They do not need to fast on Ta’anit Esther, nor do they need to make up the missed fast on a later date. Another difference, on the minor fasts, it is proper to be stringent and refrain from washing in warm water and playing music, as a sign of mourning over the Temple’s destruction (see above 7:2 and n. 3). On Ta’anit Esther, however, there is no reason to adopt this stringency.