The paper examines the doctrine of understanding in Russian idealism from the late 19th to early 20th century. The author discusses the main ontological and epistemological concepts in the philosophy of V.S. Solovyov and his follower S.N. Trubetskoy. The paper offers a historical and philosophical reconstruction of the concept of understanding based on the analysis of V.S. Solovyov's Lectures on Divine Humanity and S.N. Trubetskoy's work On the Nature of Human Consciousness. According to Solovyov, the study of understanding is possible if we presume an unconditional principle that premises being as the One. Based on this premise, it is demonstrated that the unconditional principle allows to know everything without having knowledge of each subject separately, and this, in turn, is understanding process. Trubetskoy's theory of understanding is premised on the concept of soborny (gathered) mind, which defines mind as joint knowledge about all spheres of existence. The article shows that the main position shared by the Russian thinkers is the unconditional principle serving as the basis for life and mind without which the existence of either the universal or the particular is impossible. The author concludes that such a principle is a cognitive relation to the world, which unconditionality is the condition for understanding the reality as indivisible. Understanding, as presented by V.S. Solovyov and S.N. Trubetskoy, is the true understanding of the unity of existence in all its manifestations, that is, a synthesis of the sensual, rational, moral, and aesthetic.