The famous saying "Know Thyself" is well-known as the hallmark of ancient philosophy. In Christianity this imperative assumes vital importance as a duty enjoined both by natural law and by Holy Scripture, for "they are wise who know themselves well" (Prov. 13:10). Since God created the human person according to His "image and likeness" (Gen. 1:26-27), self-knowledge is also a central path to attaining the knowledge of God. As Saint Gregory of Nyssa...