Gregory Nazianzen

Gregory of Nazianzus (c. 329–390), the third Cappadocian Father, is honoured in the East simply as “the Theologian.” Briefly archbishop of Constantinople, his Five Theological Orations gave classic expression to the doctrine of the Trinity and the deity of the Holy Spirit on the eve of the Council of Constantinople (381).

Called simply "the Theologian" for the precision of his Trinitarian language, Gregory's Five Theological Orations remain a classic statement of how the one God is three persons and how Scripture's varied speech about Father, Son, and Spirit holds together. His insistence that "what is not assumed is not healed" tied the doctrine of the Trinity directly to salvation, shaping how the church has read the incarnation ever since.