It is customary in the People of Israel since the days of the Gueonites, to fast on the thirteenth day of the month of Adar, in memory of the days that Esther fasted, prior to entering the palace of King Ahasuerus, trying to annul the decree of extermination that hung over the Jews (Book of Esther 4:16) and in memory of the fast that the People of Israel carried out on the thirteenth day of Adar of that year.

The decree of the evil Haman prescribed that on the thirteenth day of the month of Adar, all Jews would be killed, destroyed and eliminated, from children, women and even the elderly, and their properties plundered. By virtue of the miracle of Purim, the hanging of Haman and the rise of Esther and Mordechai, King Ahasuerus sent a royal letter to the entire empire, in which he allowed the Jews to defend themselves against their attackers on the 13th of Adar and to eliminate their pursuers. However, the first decree of extermination was still in place, since every edict that had the signature and seal of the royal ring could not be annulled, so that the enemies of the People of Israel could still carry out their plans. In short, the thirteenth day of Adar was the day that the enemies of the Jews were allowed to attack and exterminate the Jews, while the Jews were allowed to defend themselves from their attackers.
Although for At that time Mordechai was already viceroy, the danger on the Jews still lurked and it was still necessary for the Eternal to have mercy on us in order to overcome our enemies on the battlefield. Therefore, the Jews who could not or needed to fight did "teshuvah" (Repentance and Return to the Creator) and fasted all the thirteenth day of Adar, as tradition indicates, that in times of misfortune, it is necessary to return to the Creator. There is no better "teshuvah" than that which is accompanied by fasting, since it refines man's materiality and returns his spirituality to a central and essential aspect of his person.
This is how the People of Israel are accustomed to fasting the thirteenth day of Adar, in memory of that fast. Furthermore, we still have enemies and persecutors who seek to exterminate us, so we are still in need of fasting and teshuvah again every year.

From a ritual point of view, Esther's fast is lighter than the usual ones. other minor fasts, since the latter were decreed by the prophets while Esther's fast is the result of popular practice over the years. However, for practical purposes, there is almost no difference between the rules of the different fasts mentioned.

The religious services and the Torah reading of Esther's fast on Shacharit and Mincha are identical to those of the Other minor fasts, however, because it is the eve of Purim, "Nefilat Apaim" is not recited in Mincha (Mishna Berurá 131: 33). According to the Ashkenazi tradition, which is used to reciting the “Avinu Malkenu” prayer on Shacharit and Mincha of the public fast days, it is omitted in the case of Mincha of the Fast of Esther, due to its proximity to the festival of Purim. When the thirteenth of Adar falls on Shabbat, the fast is advanced to Thursday, so it is not carried out next to the day of Purim and therefore the Mincha service is similar to that of the other minor fasts.
(Pninei Halacha, Zmanim, Purim)

This year the Fast of Esther will fall on Thursday, February 25, and we fast from sunrise to sunrise.

The Garden of Breslev wishes you a next Purim Sameach! (Happy Purim)