The Trinity is a doctrine that some have had issue with since the earliest days of Christianity. The great Church Father, St. Augustine, was not immune to having to deal with Christological heresies. Though the heresies are Christological, they deal with the Trinity because Christ is the second person of the Trinity. If a there is a false understanding of who Christ is, then there is a false understanding of what the Trinity is. In discussing these various heresies, St. Augustine wrote a treatise titled On the Trinity. This has become known as one of his most difficult works and it took him sixteen years to complete (Augnet 2135). His work is gift to all of us and shows various arguments supporting the equality of divine persons against Christological heresies.
In chapter one, St. Augustine warns the reader of those who commit heresy through the misuse of reason. They fall into error by misinterpreting the sacred text through crude love of reason (Augustine Ch.1). By doing so they miss the point of the text and somehow twist scripture to mean something it does not intend. In all fairness, this is still something that happens today regarding the Trinity. In chapter five, Augustine speaks of the unity of the divine persons. He does this specifically by describing how the three persons are one, how they have individual work, and yet work together. Augustine states in regard to their work, “Father does some things, the Son other things, and the Holy Spirit yet others” (Augustine Ch.5.8). The Holy Spirit is the spirit of both the Father and the Son and was not begotten. Just like the Father and the Son, the Holy Spirit has no beginning or end.
In Chapter six Augustine seems to be teaching against a type of modalism that was going around. Some were saying that God was not immortal because he changed into the Son and Holy Spirit through time, or that somehow Christ was less that the Father. Augustine brilliantly answers with scripture. This is still a method that is effective today. He quotes John 1:1 to show that Christ has always existed, and that the scriptures call Him God (Augustine Ch. 6.9). He then alludes to the baptism of Christ in Matthew chapter 3 to show the unity and equality of the three. Jesus is present, it was the Father’s voice that spoke, and it was the Holy Spirit that was present in the dove. This shows that they all exist at the same time, in unity, equality, and that it is not one form changing to another.
In proving his case of equality among the Trinitarian persons, St. Augustine looks to 1 Corinthians 8:6 which states, “yet for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist” (NRSV). This verse affirms the divinity of Christ by mentioning him in the same sentence as God. Notice also how all things exist through the Father and the Son? Each person of the Trinity has a clause, or duty, assigned. One is not more important than the other, but they all work together for our redemption and salvation (Augustine 6.12).
Some may say that the verse mentioned above makes sense, but what of the Holy Spirit? In Chapter 6, St. Augustine goes to great lengths to show that the Holy Spirit is equal to the Father and the Son. The Holy Spirit is not something that had a point of origin. In other words, he is not a creature that had a beginning and that will have an ultimate end. The Holy Spirit is equal, coeternal, and of the same essence. Regarding the Holy Spirit St. Paul writes in Philippians 3:3, “For it is we who are the circumcision, who worship in the Spirit of God and boast in Christ Jesus and have no confidence in the flesh” (NRSV). Also in 1 Corinthians 6:9, St. Paul specifically mentions that our bodies are temples of the Holy Spirit. We serve, worship, and ask the Holy Spirit for things just as we would the Father and the Son. That is because they are coequal and God.
Augustine. On the Trinity From Nicene and Post-Nicene Fathers, First Series, Vol. 3.Edited by Philip Schaff. (Buffalo, NY: Christian Literature Publishing Co.,1887.) Revised and edited for New Advent by Kevin Knight.<http://www.newadvent.org/fathers/130101.htm>, accessed October 14, 2018.
Augustinians Australia. http://www.augnet.org/en/works-of-augustine/writings-of-augustine/2135-on-the-trinity/, accessed October 14, 2018.