This is a foundational text on Christology and the Trinity which was written by a fourth century bishop during a time of great theological controversy and turmoil. St. Gregory of Nanzanius (ca. 329 – ca. 390) was one of three Cappadocian Fathers who wrote this work in response to the theology of Eunomius (a form of Arianism), seeking to refute the heresy and define the relationship of Father and Son. Although this topic is of great importance, the concepts and language are difficult to understand, so this is a book more suited to scholars and serious Bible students than to the average reader.