what is purim all about

The Jews were in a sorry state back in Persia. They were fast becoming assimilated, not keeping Torah and Mitzvos. You couldn't even tell who was a Jew by looking at them, the megilla says that the only way Haman knew that mordechai was Jewish was because people told him. My chavrussa (who I am giving credit for the base idea behind the vort) said that there are some modern opinions that Mordechai and Esther were themselves assimilated.

The miracle here was not that the Jews were saved, the miracle was that they accepted the Torah anew. They all realized what happened could have only come from God and therefore did tshuva. If you look at what Mordechai did, it seems very small from a Jewish perspective. He refused to bow down to Haman. Even a jew who eats treif on yom kippur wouldn't bow down. It's one of the big 3 sins. But it was this small, almost insignificant act that brought about the grand scale tshuva which was the goal of Purim. Saving the Jews was incidental to the main goal. What we learn out from Purim is that even if there is just a spark of Judaism left in someone it can cause the entire Jewish people to ignite in a religious fervor.

Even Tommy Lapid lighting the menorah can cause tshuva. (Though if he knew that, he would shoot himself for doing it)

When I told my dad this vort, he didn't like that I said mordechai and Esther were assimilated, so I told him he didn't understand Toras Eretz Yisroel. Then I called my little brother in jerusalem and told him to tell my dad the same vort when he visited him on Purim the next day.