Abstract: This article is dedicated to the analysis of historical-philosophical transformation of the concepts of “conciliarity” (sobornost) and “all-unity” in the works of N. O. Lossky. Considering that the religious-philosophical origins of his system take roots not only in the Western and Russian Neo- Leibnizianism, but also Slavophilism and V. S. Solovyov’s philosophy of all unity, the authors determine and interpret the logical methodological and gnoseological justification of N. O. Lossky’s shift towards the notion of “consubstantiality”, which becomes the foundation for his concept of existence and hierarchical unity. It is established that N. O. Lossky, in the context of the immanence of knowledge concept, overcomes the characteristic to the classical philosophy demarcation for “Self” and “non-Self”, stating that the forming knowledge is not a prerogative of an individual entity, but the affiliation of all entities by the principle of “interconditionality” and “consubstantiality”. This approach not only defines the nature of “openness” of the mind, which is actually relevant for the modern epistemological though, but also the relationship between entities in the becoming of reality.