Mordecai wrote these things down and sent letters to all the Jews in all the provinces, both near and far, of King Ahasuerus.
References for Esther 9:20
He made it a rule that Jews keep the fourteenth and fifteenth days of the month of Adar as special days each and every year.
They are the days on which the Jews finally put to rest the troubles with their enemies. The month is the one when everything turned around for them from sadness to joy, and from sad, loud crying to a holiday. They are to make them days of feasts and joyous events, days to send food gifts to each other and money gifts to the poor.
The Jews agreed to continue what they had already begun to do—just what Mordecai had written to them.
Indeed, Haman, Hammedatha the Agagite's son, the enemy of all the Jews, had planned to destroy the Jews. He had servants throw pur (that is, the dice) to find the best month and day to trouble greatly and destroy them.
But when Esther came before the king, his written order said: The wicked plan that Haman made against the Jews should turn back on him instead. So they impaled him and his sons on pointed poles.
That is why people call these days Purim, by using the ancient word pur. It all fit with what this letter said, with what they saw happen, and with what they themselves went through.
The Jews agreed that they, their children, grandchildren, and great-grandchildren, as well as all non-Jews who become Jews, should always keep these two days. They agreed to follow the written rules—and at the proper time too—every year.
So forever every family, province, and town remembers to keep these days. These days of Purim won't die out among the Jews. They will remember to keep them forever.
Queen Esther daughter of Abihail, along with Mordecai the Jew, wrote with her full royal power to show that this second letter about Purim was correct.
References for Esther 9:29
Letters conveying good wishes and words of friendship were sent to all the Jews throughout the one hundred twenty-seven provinces in the kingdom of Ahasuerus.
Their aim was to make sure that the Jews kept these days of Purim at the proper time, following the rule that Mordecai the Jew and Queen Esther had made. The rule fit well with what they themselves had agreed to do forever and with other things they did—like fasting and lamenting.
Esther's order made these features of Purim part of the law, so it was written down.