Chapter 141:1-2 (a)
Laws of the Megillah
1. When the month of Adar begins, we increase our joy. If a Jew has a
dispute with a Gentile, he should try to arrange for the judgment to be
held in Adar (1).
2(a). During the time of Mordechai and Esther, the Jews gathered together
on the thirteenth of Adar to defend their lives and take revenge on their
enemies (2). Thus on that day, they had to petition G-d for mercy, [asking
Him] to aid them. It is customary for the Jews to fast when they are in the
midst of a war so that G-d will aid them. For example, when Moses our
teacher waged war against Amalek, he fasted. Accordingly, we can assume
that in the era of Mordechai and Esther, they fasted on the thirteenth of Adar.
For this reason, this day has been accepted by the entire Jewish people as
a communal fast and is called the "Fast of Esther". [On it,] we recall how
the Creator, blessed be His name, watches over us, and hears the prayers of
each person in his times of difficulty when he fasts and repents to G-d
wholeheartedly, just he did for our ancestors in those days (during the
time of Purim).
(1) The month of Adar is considered a favorable time for Jews.
(2) Haman had convinced the Persian king, Achashverosh, to sign a decree
allowing the Persian population to destroy the Jews on the 13th of Adar.
When Haman was hung and Mordechai appointed chief advisor in his place, the
king signed another decree allowing the Jews to defend themselves and
attack their enemies on the 13th of Adar (See the "Book of Esther").