Biography

Although there is an obvious sense in which light becomes important for Milton's own life, the light motif in Book III also has a strong biblical and theological precedent. See GS on this:

Milton introduces the character of God and Son with preparatory phrases of praise, almost a hymn, describing the nature of God and heaven. From stanzas 1-55, Milton uses the idea of light to represent this nature. Alternately, light is used to describe God himself, the first born Son, the immortality of God, the glory of God, grace, truth, wisdom, and physical light. Heaven is a place, then, full of light but much of it is an invisible light, i.e. the light of wisdom, that man cannot perceive in the same manner as physical light but which works in the same way.