Book III opens with a prologue as did Book I. This prologue is often called "The Prologue to Light" because it is addressed to the "holy light" of God and Heaven. Light here is associated with the eternal good and stands in contrast to the darkness associated with Hell and evil in Books I and II. The idea that stands out in the well-known "prologue to light" that opens Book III is how personal it is. Milton's blindness prevents him from seeing any light except the light of God, which illuminates the mind and which still allows him to be a poet. He makes references to the greatest classical epic poet, Homer (Maeonides), who according to tradition, was also blind, and to two mythic blind prophets, Tiresias and Phineas, who, even though blind, saw what others could not because of a gift from the gods.
Artistically then, Milton is able to place himself between the erudition of a classical "Invocation of Light" (as in Dante's Paradiso) and a personal, almost lyric, meditation on blindness. In the closing lines of this prologue, Milton brings the entire passage into focus as he asks for God's light to shine inwardly so that he can reveal what no man has seen. In this closing, he is able to transform the evil of his blindness into an intellectual and spiritual insight that surpasses anything possible by normal human sight. This notion of evil transformed to good is picked up thematically in the next section of Book III.
