The development of Christian theology was decisively influenced by an unknown writer of the early 6th century whose works circulated under the name of Dionysius the Areopagite, the Athenian disciple of St. Paul the Apostle (the writer is therefore often called Pseudo-Dionysius). In the writings of Pseudo-Dionysius, God is depicted as revealing himself to the created order through hierarchies of angels and through the hierarchy of the church. Pseudo-Dionysius also introduced a number of distinctions about the nature of theology that were destined to be of profound influence. His short treatise The Mystical Theology discusses affirmative and negative (kataphatic and apophatic) theologies, symbolic theology, and mystical theology. Pseudo-Dionysius borrowed the kataphatic-apophatic distinction from the great 5th-century Neoplatonist philosopher Proclus: whereas a kataphatic theology affirms what God has revealed of himself (in creation and revelation), an apophatic theology negates everything ascribed to God because human concepts and images are inadequate to describe his reality. Symbolic theology, as Pseudo-Dionysius understood it, is an extension of kataphatic theology that seeks to interpret symbols and images that are used in the Scriptures to express God’s nature and activity. Mystical, or hidden, theology seems to be the experience of the divine reality to which apophatic theology points—the equivalent of theologia in the sense in which Evagrius Ponticus used the term. This identification was made explicit by the 11th-century Byzantine theologian Nicetas Stethatos.

With the development in Western theology of increasingly sharp distinctions between nature and grace, the natural and the supernatural, and reason and revelation, theologians became interested in what truths about God could be established by reason alone. Called natural theology (theologia naturalis), as opposed to revealed theology (theologia revelata), this discipline became particularly important in arguments between Christians on the one hand and Jews and Muslims on the other, because the arguments of natural theology did not depend on the acceptance of revelation.

The systematic presentations that characterized Western theology in the 13th century (the age of the Schoolmen, or Scholastics) were often prefaced by an account of what could be established by reason about God; usually the first thing to be established was his existence. The most famous set of such arguments is the so-called Five Ways of St. Thomas Aquinas, which appears in his greatest work, the Summa theologiae (1265/66–1273). Aquinas claimed to have established the existence of God as the unmoved mover, as the ultimate efficient cause, as the necessary being, as the perfect being, and as the final cause of all beings. For Aquinas, such natural theology was part of the sacra doctrina (“sacred doctrine”) of the church.

The century following Aquinas was marked by the development of the “theology of the two powers,” which distinguished between what God can do absolutely (potentia absoluta), or logically, and what he has bound himself to do in accordance with the covenant he established with humankind (potentia ordinata). This distinction helped sharpen the division between what is necessarily so, which could be explored by reason, and what God has revealed about himself and his relations with humankind. The contrast between reason and revelation was reflected in the continued development of natural theology and revealed theology .

In the late Middle Ages a further division occurred between “rational theology” (which usually embraced both natural and revealed theology) and a theology of felt experience, often called “mystical theology,” a designation consciously borrowed from Pseudo-Dionysius. Mystical theology came to be identified with the experience of God and with contemplation of the divine. An alternative approach, known as “ascetical theology,” involved seeking God through a life of prayer, devotion, self-denial, and mortification.

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The Renaissance, the Reformation, and the Enlightenment

During the Renaissance, medieval theology suffered further fragmentation, but theologians also acquired new conceptual tools. The late-medieval conception of Christianity had emphasized its contingent nature, its truth being not a logical necessity but the result of the will of God. Although few, if any, of the thinkers of the Renaissance wished to undermine Christianity, their awareness of its contingency led them to look for some underlying truth, a “primordial revelation” that would make sense of both Christianity and the religions of classical and late antiquity. This truth was often identified with the so-called Hermetic wisdom attributed to Hermes Trismegistos (Hermes the Thrice-Greatest), the Greek name of Thoth, the Egyptian god of writing. Although Hermetic teachings were thought to be of unimaginable antiquity, in reality the writings from which they were drawn (the Hermetic writings) date from only the mid-1st to the late 3rd centuries.

The theology of the primordial revelation was called pristina theologia (“pristine theology”), or the theology of human primal innocence. Pristina theologia provided the starting point for many attempts by thinkers of the Renaissance to penetrate behind the faded texture of the religious systems of their day to what was thought to be some ultimate forgotten truth. Often it was studied in combination with mystical theology, which was thought to authenticate pristina theologia by providing a felt experience of the ultimate. Out of this potent mixture emerged the Renaissance revival of alchemy, movements such as the Rosicrucians, and the elaborately symbolic mysticism of the German thinker Jakob Böhme (1575–1624).

With the turn of the 18th century, the ideas of the Renaissance came to assume a somewhat more somber hue: pristina theologia yielded to natural religion—that is, the principles of religion that can be established by reason alone (e.g., that God exists). Natural religion was then contrasted with positive religion, or the particular religious traditions of different societies or cultures. This distinction would become axiomatic in Protestant theology during the Enlightenment and in much of the post-Enlightenment period. The Enlightenment belief in the contingent nature of revelation led scholars of the period to treat the sacred books of Christianity as historically determined rather than as witnesses to, or embodiments of, divine revelation. This conception soon created, as the German writer Gotthold Lessing described it, an “ugly, broad ditch” between the history to which the Scriptures belonged and bore witness and the eternal truths that the dogmatic systems had derived from them.