For this reason these days are known as Purim, after the name of pur.

Esther’s command established these matters of Purim, and the matter was officially recorded. ¹ 

So Queen Esther, the daughter of Abihail, and Mordecai the Jew wrote with full authority to confirm this second ¹  letter about Purim.

to establish these days of Purim in their proper times, just as Mordecai the Jew and Queen Esther had established, and just as they had established both for themselves and their descendants, matters pertaining to fasting and lamentation.

These days were to be remembered and to be celebrated in every generation and in every family, every province, and every city. The Jews were not to fail to observe these days of Purim; the remembrance of them was not to cease among their descendants.