After Haman leads Mordechai on horseback through the streets of Shushan, Haman goes home shamed. He tells over what happened to his wife Zeresh and family. They all tell him that being that Mordechai is a Jew you will surely fall before him.
Rashi explains their words to Haman. She said to him “This nation has been compared to the stars and to the dust. When they descend, they descend to the dust, and when they ascend, they ascend to the sky and the stars.”
In other words, previously you had a chance. The Jews looked like they were down for the count. But that's the thing with the jews - they are never down for the count. They can have momentary lapses where they can be overcome by their enemies, but they always rebound and when they do, nobody can overcome them.
It is a lesson repeated throughout history. The Jews get oppressed, but eventually God picks us up and we recover. Once that happens we overcome and emerge victorious over our enemies.
That is the story and lesson of Purim, in brief. if we take this lesson from Purim, we have gotten the point.