The Works of Dionysius the Areopagite, tr. by John Parker, [1897], at sacred-texts.com
MYSTIC THEOLOGY is like that ladder set up on the earth whose top reached to Heaven on which the angels of God were ascending and descending, and above which stood Almighty God. The Angel ascending is the "negative" which distinguishes Almighty God from all created things. God is not matter--soul, mind, spirit, any being, nor even being itself, but above and beyond all these. The Angel descending is the "Affirmative." God is good, wise, powerful, the Being, until we come to Symbolic Theology, which denotes Him under material forms and conditions: Theology prefers the negative because Almighty God is more appropriately presented by distinction than by comparison.
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