Letter 5 is famously short: "The divine darkness is the unapproachable light in which God is said to dwell." Get used to the paradoxes here.
The earthly mirror of the celestial text. It explains the liturgy, baptism, the Eucharist, and the consecration of priests as symbolic reflections of the angelic order. For liturgical studies, this is indispensable. pseudo-dionysius the complete works pdf