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.