The Church cannot be understood when seen merely from the outside; it cannot be rationally defined, or reduced to concepts. The Church can only be understood by those who live within it. Its life must actually be experienced, for it is not a reality of the external kind. Its intrinsic nature cannot be apprehended by those who stand apart from it. The Church is not a temple built of stone, neither is it a community of believers, nor a parish consisting of human beings, nor yet an institution juridically determined — though all these things are elements in its composition. It does not possess definite limits and external marks which determine its inner nature and differentiate it from the rest of existence. The Church possesses physical, psychical, and social elements, yet none of these define its nature. The Church is not a tangible substance belonging to the world of visible things, nor is it an empirical reality analogous to that of minerals, plants, or animals. It belongs to the world of invisible things which can only be demonstrated by faith, for it is an inner reality.
Nikolai Berdyaev, Freedom and the Spirit, p. 328