The story of Esther, and the celebration of it at Purim, celebrates at its core the triumph of good over evil, with cheering at the mention of Mordecai’s name and booing and hissing at the mention of Haman. It commemorates God’s protection of His people (here the nation of Israel) through otherwise improbable events, and the ultimate victory of God over the schemes of Satan as described in other books like Daniel and Revelation. It acknowledges God’s use of ordinary people willing to be obedient and faithful within the circumstances God has set them.
"But thanks be to God! He gives us the victory through our Lord Jesus Christ."
1 Corinthians 15:57