Megillat Esther: Establishing Purim as a Holiday

We delve into the end of Megillat Esther and examine the tension in establishing Purim as a holiday. What does it mean that Mordekhai is accepted by "most of" his brethren? What is happening when Mordekhai and Esther repeatedly send out the "letters of Purim?" How does Purim fit in with the prohibition to add to the Torah?  What is going on with the Jewish people when Purim is first established, and how does that affect their reaction to Mordekhai and Esther?