While I was reading through Nick Needham's volume 1 of 2000 Years of Christ's Power, this work by Gregory of Nazianzus was recommended for reading concerning the trinity. In this short book, Nazianzus addresses God's eternal nature, the personhood of each person of the divine trinity, and several heresies already in circulation (ie Sabellianism; the belief that God is one person, who appears as three different modes of the one person, the Father, Son, and Spirit). Nazianzus distinguishes between the persons of the godhead by using terms "unbegotten", "only-begotten", and "what proceeds from the Father and the Son" to describe God the Father (unbegotten), the Son (the only-begotten), and the Spirit (what proceeds from the Father and the Son). The language that orthodox Christians use today for the Divine Trinity clearly come from Nazianzus' thoughts and works.