Book Summary of ON THE TRINITY by Augustine

Books 1-4: The Trinity in the Creeds and Scriptures

“Some persons, however, find a difficulty in this faith; when they hear that the Father is God, and the Son God, and the Holy Spirit God, and yet that this Trinity is not three Gods, but one God; and they ask how they are to understand this: especially when it is said that the Trinity works indivisibly in everything that God works, and yet that a certain voice of the Father spoke, which is not the voice of the Son; and that none except the Son was born in the flesh, and suffered, and rose again, and ascended into heaven; and that none except the Holy Spirit came in the form of a dove. They wish to understand how the Trinity uttered that voice which was only of the Father; and how the same Trinity created that flesh in which the Son only was born of the Virgin; and how the very same Trinity itself wrought that form of a dove, in which the Holy Spirit only appeared. Yet, otherwise, the Trinity does not work indivisibly, but the Father does some things, the Son other things, and the Holy Spirit yet others: or else, if they do some things together, some severally, then the Trinity is not indivisible. It is a difficulty, too, to them, in what manner the Holy Spirit is in the Trinity, whom neither the Father nor the Son, nor both, have begotten, although He is the Spirit both of the Father and of the Son.” – Book 1, Chapter 5, paragraph 8

Augustine establishes the doctrine, not first through scripture, but through the creeds and church councils that had already authoritatively clarified the doctrine of the trinity. The Nicene creed began to resolve the Arian controversy, concluding that Jesus was co-equal with the Father. However, anti-Niceans and Arians continued the debate, which was again addressed in the Council at Constantinople in 381.

Augustine then moved on to review the core New Testament passages such as in John 1 that attest to the divinity of Jesus and the Holy Spirit. He also traces the many Old Testament epiphanies and passages that allude to the members of the Trinity, and how these fit in and reveal the redemptive mission of God to come in the New Testament, as revealed in God the Father, Son, and Spirit. Augustine also addresses objections and adds qualifications that keep us from various heretical extremes. Many of these distinctions are related to contemporary heresies that Augustine dealt with in his other writings.

 

Books 5-7: The Trinity and the Names of God

In these books, Augustine advances his arguments into ideas of form and substance, God’s immateriality, and his eternality, which includes Christ’s eternality. He proceeds to examine the names of God, including Lord and Creator, begotten vs. unbegotten, as well as the meanings of Father, Son, and Spirit, and what these titles and relationships mean. The sum of the three, for instance, is not greater than the Father. Importantly, he defines a difference between the person and essence of God, from which we get the definition of “three persons, one essence.” Lastly, Augustine sees his arguments as an ascent towards knowing God and proposes the primary assumption that the imago Dei (image of God) demands a reflection of the Trinity in the nature of man.

 

Books 8-14: The Imago Dei in Human Psychology

In books 8-14, Augustine explores his contention that the trinitarian nature of God is reflected in man, specifically the mind or soul of man. He proposes many triads, though he is not unskeptical, and often points out the possible weaknesses of each. Based on the idea that God is love (1 John 4:7), he first explores the triad of the lover, the beloved, and love itself.

In book 8, he also introduces us to the paradox of inquiry. That is, how can we discover what we do not know? That is, if we don’t know what we don’t know, we don’t even know what we are specifically looking for. The epistemological difficulties of knowing the invisible God, and even what phenomenon or ideas we should be seeking, and by what methods are a significant paradox.

Augustine goes on to elaborate at least two more major triads based on the mind of man, as well as others each based in one of the five senses, in the bodily triad of father, mother, and child, as well as other human capabilities. These two major triads are mind, knowledge, and love, as well as memory, intellect, and will. In all of these, however, he is not merely conjecturing random triads, but is evaluating them according to rules to see if they measure up to a Trinitarian-like triad:

 

Book 15: Human Weakness and the Trinitarian Imago Dei

In this final book, Augustine explores some weaknesses in this trinitarian approach to anthropology. He does not believe that such human triads prove the divine Trinity, and he admits that there is no obvious direct analogy. Augustine admits this lack of congruity with Paul’s admission of incomplete knowledge (“now we see as through a glass darkly, 1 Cor. 13:12). Augustine provides a helpful review of each of the previous chapters, and reminds us, as he has throughout, that true knowledge of God comes from devotion and interaction with God, not merely intellectual musing.