Mordecai had these events written down and sent letters to all the Jews, near and far, throughout the Persian Empire,
telling them to observe the fourteenth and fifteenth days of Adar as holidays every year.
These were the days on which the Jews had rid themselves of their enemies; this was a month that had been turned from a time of grief and despair into a time of joy and happiness. They were told to observe these days with feasts and parties, giving gifts of food to one another and to the poor.
So the Jews followed Mordecai's instructions, and the celebration became an annual custom.
Haman son of Hammedatha - the descendant of Agag and the enemy of the Jewish people - had cast lots ("purim," they were called) to determine the day for destroying the Jews; he had planned to wipe them out. 1
References for Esther 9:24
But Esther went to the king, and the king issued written orders with the result that Haman suffered the fate he had planned for the Jews - he and his sons were hanged from the gallows.
That is why the holidays are called Purim. Because of Mordecai's letter and because of all that had happened to them,
the Jews made it a rule for themselves, their descendants, and anyone who might become a Jew, that at the proper time each year these two days would be regularly observed according to Mordecai's instructions.
It was resolved that every Jewish family of every future generation in every province and every city should remember and observe the days of Purim for all time to come.
Then Queen Esther, the daughter of Abihail, along with Mordecai, also wrote a letter, putting her full authority behind the letter about Purim, which Mordecai had written earlier.
The letter was addressed to all the Jews, and copies were sent to all the 127 provinces of the Persian Empire. It wished the Jews peace and security
and directed them and their descendants to observe the days of Purim at the proper time, just as they had adopted rules for the observance of fasts and times of mourning. This was commanded by both Mordecai and Queen Esther.
Esther's command, confirming the rules for Purim, was written down on a scroll.