The book briefly outlines the important teaching of the great holy father of the Orthodox Church, St. Gregory Palamas (1296–1359) about the difference between essence and energy in God. This teaching has been inherent in church theology since early times and points to the ideal of Orthodox spirituality - salvation, deification and vision of God, partly achievable for man even on earth. In this edition, this teaching is placed in the broad context of the patristic teaching about the knowledge of God and its types - revelation and natural. The author-compiler also touches on the moral conditions of knowledge of God.