The purpose of commemorating the day with the word Purim is to remember that God providentially delivered the people of God from the clutches of Haman. In Esther 8-10, we read how God rescued his people, but the rescue points to a more incredible rescue.
The book of Esther is a sobering reminder that there is a battle between good and evil in this world, and sometimes the faces of evil are those in authority. But here is the deal. Even though you have earthly authorities - good and bad - there is One who has ultimate power over this world and the entire universe!
On what other basis do Mordecai and Esther have to believe the Jews will not be wiped off the planet? A hunch? A false hope? Or is Mordecai and Esther remembering the faithfulness of God?
There are times when a person exists in a corrupt system or is directly confronted by an evil person. In Esther 3, we see both.
The Book of Esther is not what you think. When some people think about the Book of Esther the Book of Ruth comes to mind. Both are named after women. And both are in the Old Testament. But that is where the comparison ends. Ruth is a story of sacrifice, loyalty, and love. There are plenty of Christological connections in Ruth. In contrast, Esther is dark. There is heavy drinking, sexual immorality, and a genocidal plot. God is never mentioned in Esther. Yet, Esther is unlike any other book in the entire Bible, because the providential hand of God is at work.
The Book of Esther is about the providence of God engaging with people, and the world, even when God is not recognized or mentioned.