GREGORY OF NAZIANZUS (c. 329–c. 391) was one of the Cappadocian fathers, known to Christian tradition as "the Theologian" by virtue of his rhetorical erudition and the consummate skill with which he combated the perceived heresies of those who in any way detracted from or denied the validity of the established orthodoxy of his day. One of those "heretics" was his own father, Gregory the Elder, who in his youth had been a member of an obscure but apparently popular sect known as the Hypsistarii. But inasmuch as his father was later converted to orthodoxy and subsequently consecrated bishop, his son could say of him that he was one whose "character anticipates their faith" (Oration 18) and that he was "well grafted out of the wild olive tree into the good one" (Or. 7). It was by his mother, Nonna, however, that Gregory was to be most...