Mordechai and Esther

What makes Purim a special yom tov and why is it a day of festivity and celebration? Why is Purim unique as opposed to other days of Jewish salvation? Why is the megilla called Megillat Esther and not Megillat Mordechai? A close examination of the Purim story within its historical context provides answers to these questions, by understanding Purim as a celebration of the renewal of the covenant between Israel and God.