Chapter 1 explores the beginning of Russian religious thought in light of the relationship between faith and reason, Christian revelation and ancient philosophy. Two tendencies in Eastern Christian cosmology, reflecting two of the aspects (the transcendent and the immanent ones: the divine essence and the divine energies) of God are analyzed. The first one is typical for, and supposes that there is a clear-cut borderline between, the divine essence and creation and, respectively, between theology and science. Consequently, the task of philosophy is nothing other than to expose the limits of human reasoning and especially scientific knowledge. The second tendency claims that since the divine energies penetrate the empirical realm, therefore, cosmology is considered a part of theology. In Medieval Rus both approaches concerning the possibility of cognition of God through creation and, as one of the consequences, a link between theology and science, were adopted.