This book (from a series of works by St. Theophanes the Recluse) is compiled in a systematic form and, to facilitate reading and perception, is provided with detailed headings, many notes and comments, mainly by modern scientists, philosophers and spiritual writers. The book is addressed to a wide range of Orthodox readers, as well as workers of science and culture sympathizing with Orthodoxy, but can be used as a teaching aid for theological schools and scientific and religious seminars.