Contributed by: Rabbi Haim Shaul
Why do we fast?
In the days of Mordechai and Esther, Jews gathered on the thirteenth of Adar to stand united against their enemies. It was on that day that they fasted and prayed to Hashem to save them from the cold hand of anti-Semitism they faced, similar to the time of Moshe Rabenou, who prayed and fasted the day Bnei Yisrael fought against Amalek. Just as Hashem heard the prayers' of Moshe, He heard the prayers of the Jews in the time of Mordechai. Not only was the day victorious in that the evil plot of Haman was foiled, but that the day of Purim changed to be a day of happiness and joy. The Jews fought back against their oppressors, with Hashem help and guidance.
Therefore, we fast. In remembrance of that awesome day that the Jews stood united, prayed to Hashem for help, and were answered.