As already noted, [Jacob] Thomasius was not just a critical historian of philosophy. First and foremost, he was a pious Lutheran who believed that the biblical revelation was the only reliable source of religious truth and who saw the history of Christianity from the patristic period to the Reformation as a history of error and degeneration, along the general lines of the “Magdeburg Centuries.” However, whereas Flacius Illyricus and his collaborators had pointed to the papacy as the diabolical cause of Christian perversion, for Thomasius the ultimate source of heresy was pagan philosophy, and platonism in particular. Having read Crispo and other critics of the Platonism of the Fathers, the patristic apologists were no longer a stumbling block for Thomasius: it was clear to him that by misinterpreting platonic philosophy as compatible with Christian faith they had introduced the virus of Hellenistic paganism.
But what was it, precisely, that made pagan philosophies so utterly alien to biblical revelation? Historically, Thomasius traced all of them to their origin in the dualistic doctrine of Zoroaster and the Persian Magi, which in turn had been inspired by the devil: it was from this barbarian source that philosophy had reached Pythagoras, Plato, Aristotle and the other Greek philosophers. But this dualism, in turn, reflected the “original fallacy” (Πρῶτον ψεῦδος) on which the whole of pagan philosophy was based: its conviction that “it is impossible for anything to be born out of nothing.” The true core of all pagan error was, in other words, its rejection of the doctrine of creatio ex nihilo, in favor of the eternity of the world. Against the biblical distinction between God and the world, or Creator and creation, paganism made the world eternal like God himself. All heretical beliefs were ultimately grounded in this belief: emanationism (souls or intelligences are not newly created by God but pour forth from his eternal essence), dualism (form and matter, or God and matter, are two co-eternal principles), pantheism (the world is God), and materialism (God is the world). In their different ways, all these variations amounted to deification of the creation at the expense of its Creator.
For Thomasius, the temptation of man by this ultimately diabolical doctrine of pagan philosophy was a direct parallel to the temptation of Adam and Eve that had resulted in the Fall, and accordingly, the Christian revelation was presented by him as its radical salvational counterpart. But although the coming of Christ should have spelled the end of paganism, through the devil’s machinations its basic philosophical doctrine succeeded in infiltrating Christian theology, particularly in the form of platonism. Any such continuation of pagan philosophy under the guise of Christianity was understood by Thomasius as a case of syncretism, and thus as heresy, whether it occurred in the Fathers and Roman Catholic doctrine or in the various forms of gnosticism and other sectarian movements that had sprouted from the “arch-heretic” Simon Magus. As a result, the entire history of the Church prior to the Reformation became synonymous with the history of heresy. […] We find ourselves back, then, with the basic opposition between history and truth. I argued in the first chapter that the Renaissance narrative of Ancient Wisdom was based upon the paradoxical concept of a history of truth. Thomasius’ Protestant counter-narrative, in contrast, recognized that ultimate religious truth cannot be subject to change and development without losing its absoluteness, and therefore cannot have a history. It followed that the history of thought could only be a history of error.
Thomasius considered the Reformation as the most thorough attempt at a de-Hellenization of Christianity thus far, but in his own century he was concerned about seeing the pagan heresies of platonism making their comeback even in Protestant contexts. He predicted, quite accurately, that these forms of heterodox spiritualism would spread ever more in the decades to come. The central characteristic of this new development was “enthusiasm” (Enthusiasmus, Schwärmerei), that is to say, the extreme emphasis on personal religious or even ecstatic experience at the expense of doctrinal belief. Like all manifestations of heresy, enthusiasm was based upon the core error of the eternity of the world: in this case in the form of the platonic doctrine of emanation and restitution, which held that the soul has its origin in an eternal, divine substance and will return to it again. Emanationism implied that human beings could return to God by attaining direct experiential knowledge of their own divine nature, by means of “ecstatic” states of mind, and this was clearly equivalent to the quintessential gnostic heresy of auto-salvation and deification by means of a salvational gnosis. Hence Thomasius was able to draw a straight line from Simon Magus and the various gnostic sects in the early history of the Church, all the way to the enthusiasm of spiritualist and early pietist currents in his own time. Next to the eternity of the world, the ψευδώνυμος γνῶσις, or “gnosis falsely so called,” was highlighted as the second core aspect of pagan heresy in Thomasius’ synthesis, and an analysis of the notion of γνῶσις τῶν ὄντων (knowledge of the things that are, that is to say, of the world as an eternal substance) was central to the Schediasma Historicum. Furthermore, by associating it with the vain search for worldly knowledge known as curiositas, he was able to suggest a close connection with the pagan “sciences” of magic and astrology (an argument that was, of course, all the easier because he had highlighted Zoroaster, the inventor of magic, as the originator of pagan philosophy).
On the basis of Thomasius’ argument, heresy could now be defined as any form of syncretism between Christianity (grounded in the doctrine of creatio ex nihilo and strict biblical faith) and pagan philosophy (grounded in the doctrine of the eternity of the world and the pursuit of gnosis). The Schediasma Historicum was a technical Latin treatise intended for academics, with a structure (short numbered paragraphs in logical sequence, plus many often lengthy notes incorporated into the text at the end of each paragraph) that made it difficult to read; but its significance was recognized by influential contemporaries such as Leibniz, Bayle, and Thomasius’ own son Christian, who all studied it carefully. For our concerns, most important is the fact that it laid the conceptual foundations for the landmark book that gave birth to the study of Western esotericism as a specific domain of research: Ehregott Daniel Colberg’s Platonisch-Hermetisches Christenthum of 1690–1691.
Anybody who opens Colberg’s book should be prepared to enter a dogmatic battlefield in the company of an author who is shooting to kill. The work consists of an uncompromising and frontal attack against what was known as the “fanatical” or “enthusiastic” theology typical of the milieus of Reformation spiritualism, with strong emphasis on Paracelsianism, Weigelianism, Rosicrucianism, and Christian theosophy in the tradition of Jacob Böhme. Considering Colberg’s extreme hostility to these currents and their ideas, and the fact that he studied them not for their own sake but in order to destroy their credibility, what is it that makes him into a pioneering figure in the study of Western esotericism? The answer is that his book was the first one to outline a complete and internally consistent historiographical concept that connected everything nowadays studied under that rubric: not only did Colberg draw lines of continuity from the platonic and hermetic currents of late antiquity through those of the Renaissance and onward to the present day, but he managed to do so on the basis of a clearly formulated theory of how and why they were all hanging together. In short, “Platonic-Hermetic Christianity” emerged from Colberg’s book as a specific religious domain with an identity of its own – not by virtue of its supposed participation in a timeless realm of metaphysical truth, but on the basis of an analysis of what had been believed and proclaimed by its historical representatives.
– Esotericism and the Academy: Rejected Knowledge in Western Culture (2012), pp. 104-8