A City of Two Tales
Short version: There are two stories of one city that make up the megillah. There's the Arabian Night style loud, colorful, wordy, wild and crazy, fast paced, party hard story. Then there's the Esther and Mordechai, man and woman of few words and details, story: She doesn't take extra make-up, she speaks poetically and to the point, his drama is described with checked off actions, at the gate, wearing sackcloth.
The power of this tale is that the subplot eats the main plot alive and then becomes the story itself. This is where divine providence comes in and why today's a holiday. When it says the king couldn't sleep it means The King could no longer sleep (so to speak). At that moment The King takes the king into his hands. Soon these two stories cross paths so that they can collide and it becomes clear that Esther got to where she was so that we could be here today.
Adapted from Poetry With A Purpose - Biblical Poetics and Interpretations by Harold Fisch.