In the first month (that is the month of Nisan), in the twelfth year of King Ahasuerus, they cast the pur (that is, ‘the lot’) in the presence of Haman from day to day and month to month, up to the twelfth month, which is the month of Adar.
But the Jews that were in Shushan had assembled on the thirteenth and on the fourteenth and on the fifteenth they rested, making it a day of feasting and gladness.
as the days when the Jews got relief from their enemies, and as the month when their sorrow was turned into joy and their mourning into celebration. These were to be days of feasting, celebration and sending presents of food to one another and giving gifts to the poor.
the Jews established and took upon themselves, upon their descendants, and upon all who joined with them, that they would commemorate these two days in the way prescribed and at the appointed time every year.