'As the soul fills the body, so G-d fills the world.'
Talmud, Berachot 30a
The turning point in the story of Purim comes with the opening verse of Chapter Six in the Book of Esther: That night, the king's sleep was disturbed.... Achashveirosh's sleepless night set in motion a series of events that led to Mordechai's rise, Haman's downfall, and the salvation of the people of Israel. Thus it is customary that in the public reading of the Book of Esther on Purim the reader raises his voice when he comes to this verse to indicate that this point marks the beginning of the miracle of Purim.
The Torah is more than a chronicler of events and a legislator of laws within the external meaning of its verses lie layer upon layer of significance, describing the essence of the human soul, of creation and reality, and of G-d's relationship with our existence. In the words of Nachmanides, The Torah discusses the ephemeral reality and alludes to the supernal reality. The same is true of the events recounted in the Book of Esther: in the supernal version, King Achashveirosh is the King Who the End and Beginning are His, and Esther is His bride, the people of Israel.
The state of galut (exile), in which G-d's chosen people are subject to alien powers and exposed to danger and persecution in which the righteous suffer and the wicked prevail is a state of sleep of the supernal King. Physical sleep brings about a distortion of the bond between body and soul and a topsy-turvy state of affairs within the human being: the sleeper's higher faculties, such as his intellect and sensory tools, are fuzzy and incoherent, while his lower faculties are unaffected; some of them (e.g., the digestive system) even function better during sleep. Sleep is thus the metaphor for a state of affairs in which the connection between the Soul of the World and the body of creation is likewise distorted. G-d grants existence and life to His creations in a manner that is much like the soul/body relationship during sleep: the good inherent in man is unfocused and obscured, while the baser elements of man and humanity flourish.
But That night, the King's sleep was disturbed. That night the Almighty woke from His slumber restored His true priorities vis-a-vis the various components of creation.
From a discourse delivered by the Rebbe on Purim 5743 (1983)