The theme of Purim and the Megillah is Hester Panim, the hiding of the Divine. God’s name does not appear in the Megillah. The miraculous salvation of the Jews doesn’t seems might like a coincidental chain of events that happen to come together in just the right way to produce the successful results. God is hidden in the normal course of nature.
The word “Megillah” is derived from the Hebrew root meaning “reveal”. Why is the ultimate book of “hidden” called by the name “revealed”? The lesson here is that God is revealed within nature, but only to those that choose to seek Him out and see him. When we look at a sunrise, we can see it as the “hand of God”, or just as a normal occurrence of nature. Nature is part of God, an expression of His constant involvement with His creation.
The lesson of the “Megillah” is that God is actually revealed, to those that make the effort to see Him.