Situated on the boundary between Western and Eastern Christianity and bordering the territories controlled by the Ottomans, Polish-Lithuanian Commonwealth was religiously and ethnically plural by its nature. In the Commonwealth, Roman Catholics (predominantly Poles and Lithuanians) comprised less than a half of the population, while Orthodox Ruthenians (Ukrainians and Byelorussians) represented the other half. Numerous communities of Jews and Armenians were located mostly in towns (especially centers of long-distance trade). Reformation and Counter-Reformation movements became the main factors that brought dynamism into religious life of the country in the 16th century. Driven by missionary zeal, Catholic religious thinkers (especially Jesuits) started to put into question beliefs and practices of the Orthodox Ruthenians. Adapting thoughts and forms of the Latin West, the Kievan Metropolitan Sea proved it had inner resources to reform, rather than to disintegrate: religious polemic and philosophical texts of the 16th – 17th centuries were among the elements of this response, and represent the main group of sources for this research.
Using the concept of "tradition," the research will demonstrate how the "tradition" became an important strategic tool in the religious struggle and in strengthening of religious identity. Questioning the idea of "tradition" being "passed down," makes possible to trace the process of construction of the "tradition" and its use for particular ideological purposes. In addition, "purity" and "purification" are the terms used in the polemics and one more goal of the project is to investigate the role and meanings of these concepts in the religious context of Polish-Lithuanian Commonwealth.