The article is a comparative analysis of the philosophical and anthropological ideas inherent to Christianity and Islam. The researcher considers Christianity and Islam as cultural traditions sharing specific features since the early Middle Ages. The author argues that their philosophical conceptions of the human being's relation to God brings these religions much closer together. On the basis of texts of the Greek-Byzantine Church Fathers, the article traces the formation of such fundamental ideas as human freedom and Divine predestination, deification and achievement of spiritual freedom, in particular, through the Uncreated Light. The author compares the concepts of Eastern Christian Church Fathers mostly with the postulates of the traditional theology of Islam (Kalam).