The article examines the relationship between cultural phenomena and the emergence and expansion of ascetic Protestantism. More specifically, it explores the cultural roots and conditions of original, early Calvinism, as distinguished from its own influences and ramifications in culture and society in general mostly emphasized in the current sociological literature. Calvinism is therefore treated not only as a conditioning and explanatory factor in cultural and other social respects, as largely done in the literature, but also as a culturally and socially overall conditioned and explained variable. This article posits and shows that the overarching and cardinal cultural root and condition of orthodox Calvinism is pre-modern medieval irrationalism, including religious and related superstitions and fanaticism. It therefore rediscovers Calvinism in the new light (or rather darkness) of being originally the effect and subsequently the system of perpetuation of medieval cultural irrationalism, in particular religious superstition and fanaticism. The intent of this article is to contribute to a better understanding, explication, and prediction of the cultural and related social causes and effects of Calvinism in the sociological literature.