He left four crucial works behind: (1) De divinis nominibus, (2) De mystica theologia, (3) De caelesti hierarchia, and (4) De ecclesiastica hierarchia. In (1) he argues that the names of God provide us with symbolic knowledge of God, but that the divine essence is unknowable to us. The names describe God’s activity, not his being—a point stressed by the Cappadocian and Alexandrian fathers. (2)  Mystical union of God, given God’s ineffability, consists in human being’s absolute ignorance of him. This idea guided spirituality along the path of theologia negativa and to reach God is to discover darkness—epistemologically speaking. Works (3) and (4) paint a picture of reality in which the structure of creation leads upward, step-by-step to God. This is expressed both, in (3) in the heavenly realm and in (4) in the order of Church government. The goal of these hierarchies is union with God. Knowledge and enlightenment pass downward on the opposite trajectory, descending from God through the various levels of angels in (3) and from God through the church and monasteries in the various levels in (4).

P.-D.’s synthesized Neoplatonist philosophy with Christian theology, providing a model for later Christian thinkers. His spirituality and ecclesiology deeply influenced medieval thinkers, most notably Maximus Confessor and Thomas Aquinas, and many commentaries were composed upon his works.