(Now this used to be the customary way to finalize a transaction involving redemption in Israel: ¹  A man would remove his sandal and give it to the other party. ²  This was a legally binding act ³  in Israel.)

to have them observe the fourteenth and the fifteenth day of the month of Adar each year

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

They see delusion and their omens are a lie. ¹  They say, “the Lord declares,” though the Lord has not sent them; ²  yet they expect their word to be confirmed. ³ 

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.