1853-1900 1871-1944 19thcentury 20thcentury biography bulgakov clergy clergyrusskai︠a︡pravoslavnai︠a︡t︠s︡erkovʹ doctrines doctrinesorthodoxeasternchurch feodor history historyrusskai͡apravoslavnai͡at͡serkovʹ russia sergiĭ sergiĭ solovyov sovietunion theologians theology vladimirsergeyevich