A part of the vast and muti-volumed ‘History of the Russian State’ was a description of the pre-Christian Slavic religion and the history of Orthodox Church in Rus’. The author considered that in the base of the old Slavic religion there was general veneration of god, for whom they did not built temples; and he believed that Slavs attributed Evil to Chernobog (Black god) depicted as lion. On the K.’s opinion, the Slavic beliefs impressed with the might of various gods. The author mentions Perun, Khors, Dazhdbog, Stribog, and accepts the existence of such gods, which later was proved to be historiographic constructs. In the story of the Christening of Rus’ the author stressed that the genuine reasons of Prince Vladimir were known to God, not to people. In his interpretation of the history of Church K. tries to show the interrelations between ecclesiastic and state institutes: for instance, he shown how the high clergy provided the legitimacy of the princes’ authority. Besides, that legitimacy was supported with the existence of princes-martyrs. The author demonstrated it on the example of St Boris and Gleb. He also described a political mechanism of participation of the high clergy in conflicts on the territory of Rus’. He stressed the high level of religious mentality and the influence of Orthodoxy; as an example, he mentioned the protests against the Ferrara and Florence Union.