Purim, the "Festival of Lots", commemorates the events which took place in the Persian royal city of Susa, Shushan in Hebrew, during the reign of King Achashverosh (thought to be Artaxerxes). The story is recounted in the Scroll of Esther.
The king’s Grand Vizier, Haman, had a very big ego and had a decree passed that everyone bow down whenever he passed through the streets. One person didn’t comply – he was Mordechai, a Jewish courtier – and it was because, as a Jew, he could bow to no one but G-d. This infuriated Haman, who persuaded the King that, by extension, all of his Jewish subjects were a threat to royal authority. He asked that all the Jews in the Empire – comprising 127 provinces – be executed and cast a lottery to determine the date. The day chosen was the 14th of Adar. Royal proclamations were sent out announcing this fact.
In the meantime, the king was having relationship problems. Having ordered his wife, Queen Vashti, to appear before his drunken court during the course of a six-month-long feast, and received her refusal to do so, he divorced and banished her. He therefore was in need of a new wife and chose one through the process of an enormous beauty pageant. The new Queen was Esther, the niece of the aforementioned Mordechai, who kept her religion a secret.
On being informed of the plan to kill all the Jews, Mordechai and Esther worked out a plan by which she would appeal to the king for clemency for her people. This carried some risk to herself, as she would be approaching the king without prior invitation, and he could well order her execution. She took the risk, blew her cover and, in presenting the matter as a personal threat to herself, enlisted the king’s sympathy. Not only that, when Achashverosh demanded to know who would dare to harm the Queen, and was told by her that it was Haman, he exploded with rage and ordered his immediate execution.
Esther and Mordechai received the king’s permission to write to all the Jews telling them to defend themselves on the chosen day, which was fast approaching. They did so, and therefore participated in their own rescue.
To celebrate and commemorate this great event, all Jews, from that day to this, read the story twice [evening and morning] on the 14th of Adar, give charity, send gifts of food to friends and eat a festive meal. During the reading of the Scroll, it is customary to drown out Haman’s name with noise each time it is read to show that oppressors will never gain the upper hand.