Under No Duress
Many times, enemies wanted to exterminate the Jews, and they were saved only at the last minute. Of all these miracles, why is only Purim celebrated with a yom tov? There was something special about Purim. Besides being delivered physically, the Jews were also delivered spiritually at this time. They accepted Hashem's Torah wholeheartedly, without any reservations. Seeing the tremendous spiritual renaissance that this miracle produced, the sages felt that it should be commemorated by a special yom tov. Although the Jews accepted the Torah on Shavuous when it was given on Sinai, they were actually under duress at the time. Their lives were in Hashem's hand and they knew it. If they did not accept the Torah, they knew that their graves would be right there in the desert. But on the first Purim the Jews were already victorious, and under no duress. In the midst of their great celebration, they reaffirmed their acceptance of the Torah without reservation.