Mordecai recorded these events and sent letters to the Jews near and far, through out al the provinces of King Xerxes, calling on them to celebrate an annual festival on these two days. He told them to celebrate these days with feasting and gladness and by giving gifts of food to each other and presents to the poor. This could commemorate a time when the Jews gained relief from their enemies, when their sorrow was turned into gladness and their mourning into joy. ( vv. 20-22, NLT)
Haman…the enemy of the Jews, had plotted to crush and destroy them on the dated determined by casting lots (the lots were called (purim). But when Esther came before the king, he issued a decree causing Haman’s evil plan to backfire, and Haman and his sons were impaled on a sharpened pole. That is why this celebration is caused Purim because it its ancient word for casting lots.
So because of Mordecai’s letter and because of what they had experienced, the Jews through out the realm agreed to inaugurate this tradition and pass it on to their descendants and to all who became Jews. The declared they would never fail to celebrate these two prescribed days at the appointed time each year. (vv. 23-27, NLT)