Sometime at around the 5th or 6th century A.D., a Christian monk sat down and penned several works on 'mystical' theology. Passing himself off as the famous Athenian convert to Christianity who heard St Paul in Athens, the works of this monk became the foundations upon which later great Christian mystics such as Meister Eckhart, the author of the Cloud of Unknowning, St John of Cross, Nicholas of Cusa, St Bonaventure, Richard of St Victor, and many others would base their 'ascents' to God.
The two most important works on the Corpus are the 'Mystical Theology' and 'The Divine Names.' Probably using the language and concepts of Neo-Platonism and in particular of Proclus along with ideas he got from reading Gregory of Nyssa, Denys expounds the 'via negativa' apprach to God.
In the mystical theology Denys outlines how Moses ascended to God through a dark 'cloud of unknowing' and reached the ineffable Godhead who is beyond all concepts, ideas and words. In the view of Denys, even in a 'clear' vision of God we do not get a clear vision of God but rather only see a 'dazzling darkness' which is above and beyond every possible concept and idea we could have of God, or any name we can apply to God. Denys seems very keen to protect the mystery of God's transcendant being, which even when 'naked' and exposed by stripping it of all concepts and ideas and names, is still completely hidden by virtue of its transcendance.
Denys explores these ideas further in 'The Divine Names', a very important work both in mysticism and theology. Denys talks of what names can be said to apply to God and he also discusses how God's goodness 'flows out' of itself to create the universe and all beings (which he calls theophanies) and which return back to God in a circular procession. This little work would have a profound effect on many of Christendom's most creative and innovative thinkers, from Scotus Eriugena, Maximus Confessor, Thomas Aquinas, St John of Cross, St Bonaventure, Robert Grosseteste and Nicholas of Cusa. Its influence still continues to this day and seems to be undergoing a kind of renaissance amoung theologians such as Von Balthasar, Karl Rahner and Valdimir Lossky.
The works which follow are somewhat weaker in both literary and theological merit. The Celestial heirarchy and the Ecclesiastical Heirarchy are attempts to fuse Neo-Platonic symbolism and angelology with Christian angelology and liturgical symbolism. His letters are somewhat edifying and refer a lot to lost works, however they were probably not written to the people he addresses them to since modern scholarship has shown Denys lived long after the New Testament was formulated canonically, and all the Apostles were long dead.
However, these weaknesses do not detract from the theological brilliance of Denys, who manages to fuse the better aspects of Neo-Platonic Philosophy with the deepest and most profound Christian theology and mysticism, without leaping to the frenzied visions of the Gnostics, nor reducing God to anthropomorphism. His spirituality is very ethereal at times and while his excesses can mislead the contemplative into over-valuing the spiritual world over the material, it should be remembered Denys also stresses God's infinite and ineffable beauty which is radiated in his glory and goodness, which makes the created universe and all beings (human and angelic) beautiful as well. He has a positive view of the incarnation and of the world, and in my view still represents one of the best mystical theologies in the Christian tradition, and in terms of world religious philosophy, offers one of the most inspiring visions of the Absolute.