In the introduction the author mentions that his interest to the Reformation was connected with the attention of students – mostly of Polish origin – to the course made by him at the Warsaw University in 1879-1880. On the author’s point of view, the success of Protestantism was explained not only with religious, but in a great scale with social reasons. He interpreted the Reformation in Poland as a result of complicated relations of local nobility and clergy. He makes an accent at the social, not at the religious components, speaking about the premises. Particularly, he compared the Reformation in the Holy Roman Empire with the Great French Revolution. He considered the Reformation as a product of some ‘damage’ of ecclesiastic institutes, as well as with a social opposition. In the Empire that process depended on two circumstances. On the first hand, it was the specific of religious spirit; on the second hand, of the serious pressure from the Papacy. So, he made accent at the German peculiarity of the Reformation. Unlike the Holy Roman Empire, in Poland there were no national opposition to the Papacy, and there were no national Protestant leaders. In the situation of diversity inside Protestantism, it led to the fast weakening the Protestant ideas and strengthening the Jesuit Order. The Reformation cracked the history of secularization of European culture in the epoch of the Renaissance and the rationalistic Enlightenment of the eighteenth century – K. treated it as a continuation of Humanism.