Our earliest explicitly Trinitarian teaching is Saint Hippolytus’ Against Noetus. While he is not the first saint to make observations consistent (or seemingly inconsistent) with later Christology and Pneumatology, he is the first to specifically write a work on the subject specifically.
It should be noted that Tertullian likewise wrote a Trinitarian work, but he is not canonized.
My overall impression of the work is that even as late as the third century, Christian Trinitarian theology was in a nascent, humble stage where not much changed from the time of the Apostles. Christians affirmed each Person as God. They likewise affirmed there was only one God. Otherwise, they did not try to make much sense of it.
Making sense of it all seemed to cause trouble. In fact, early speculations as to how this worked such as that of the Gnostics (the Logos and Spirit were Aeons emanated from God) and Modalists (the Son and Spirit were different modes which God would act under) were clearly wrong in that they compromised the actual divinity of the Son and Spirit.
But, how are we to explain something that is true which we only vaguely understand as:
[T]here are three that bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one. (1 John 5:7)
Apart from Nicene terminology, how can one in isolation even know what this means?
We see Hippolytus venture an explanation (explicitly by intention) from the Scriptures alone, simply unaware of any traditional explanation (or simply feeling that invoking any recent authorities like Irenaeus would not be convincing to his audience). He does this within the context of denouncing the doctrines of Noetus, a modalist.
We can glean from his highly Biblicist Trinitarian theology a Platonist mindset of the Father being the Mind who wills the Word. He does not go as far as Augustine, who either intentionally or coincidentally borrows the same theme, in making it abundantly clear that the “will” is in fact the Spirit. In one section, Hippolytus goes as far as to say the Spirit precedes the Son, though this appears to be a reference to the incarnation. Nevertheless, we see a Pneumatology eerily similar to Augustine’s and Damascene’s, where the Spirit’s manifestation is His resting in the Son when the will of the Father for the Son’s generation is completed.
Perhaps the last observation worth noting is that Hippolytus affirms all the necessary Christological doctrines which were to become future battlegrounds. He asserts that Jesus Christ shared had the same will as the Father, which has implications pertaining to His human will mirroring the divine will. Further, he also asserts that Jesus voluntarily died on his own authority, a Christologically pivotal speculation as it shows that an enhypostasisized and sinless being would have to will death for it even to occur.
As follows are some highlights and my comments—
The doctrine of Noetus necessitates the view that the Father suffered on the cross, which is of course absurd:
See, brethren, what a rash and audacious dogma they have introduced, when they say without shame, the Father is Himself Christ, Himself the Son, Himself was born, Himself suffered, Himself raised Himself. But it is not so. (par 3)
The incarnation, with the fullness of deity dwelling bodily in Jesus Christ, enables us to say that “God is in you,” as “in humanity.”
And in [the Scriptures] saying, “God is in you,” he referred to the mystery of the economy, because when the Word was made incarnate and became man, the Father was in the Son, and the Son in the Father, while the Son was living among men. This, therefore, was signified, brethren, that in reality the mystery of the economy by the Holy Ghost and the Virgin was this Word, constituting yet one Son to God. (par 4)
Hippolytus differentiates between the preincarnate Logos (which he often calls “Spirit,” though perhaps the Greek lacks the definite article and perhaps he is simply citing John 4:24) and the Word made flesh. However, this can be confusing because he sometimes calls the “Holy Spirit” simply Spirit—which taken at face value would seem that Hippolytus views the preincarnate Logos and the Holy Spirit to actually be the same thing and only after the incarnation can one differentiate between one or the other:
Will he say, forsooth, that flesh was in heaven? Yet there is the flesh which was presented by the Father’s Word as an offering, — the flesh that came by the Spirit and the Virgin, (and was) demonstrated to be the perfect Son of God. It is evident, therefore, that He offered Himself to the Father. And before this there was no flesh in heaven. (par 4)
And what is it that is begotten of Him, but just the Spirit, that is to say, the Word? But you will say to me, How is He begotten? (par 16)
Sadly, there is not simply not enough detail in the work for one to surmise any explicit theology of the three Persons before the incarnation.
The work makes frequent allusions to the “will” of the Father. They are not always consistent. For example:
[T]here is no one who sees God except the Son alone, the perfect man who alone declares the will of the Father. (par 5)
God, subsisting alone, and having nothing contemporaneous with Himself, determined to create the world. And conceiving the world in mind, and willing and uttering the word, He made it; and straightway it appeared, formed as it had pleased Him. For us, then, it is sufficient simply to know that there was nothing contemporaneous with God. Beside Him there was nothing; but He, while existing alone, yet existed in plurality. For He was neither without reason, nor wisdom, nor power, nor counsel. And all things were in Him, and He was the All. When He willed, and as He willed, He manifested His word in the times determined by Him, and by Him He made all things. When He wills, He does; and when He thinks, He executes; and when He speaks, He manifests; when He fashions, He contrives in wisdom. For all things that are made He forms by reason and wisdom — creating them in reason, and arranging them in wisdom. He made them, then, as He pleased, for He was God. And as the Author, and fellow-Counsellor, and Framer of the things that are in formation, He begot the Word; and as He bears this Word in Himself, and that, too, as (yet) invisible to the world which is created, He makes Him visible; (and) uttering the voice first, and begetting Him as Light of Light, He set Him forth to the world as its Lord, (and) His own mind; and whereas He was visible formerly to Himself alone, and invisible to the world which is made, He makes Him visible in order that the world might see Him in His manifestation, and be capable of being saved. (par 10)
He made them speak by the Holy Ghost, in order that, being gifted with the inspiration of the Father’s power, they might declare the Father’s counsel and will. (par 11)
If, then, the Word is sent by Jesus Christ, the will of the Father is Jesus Christ. (par 13)
In the preceding, we can see that the incarnate Logos expresses the Father’s “will.” (par 5) Then we have par 10, which similar to Augustine speaks of the Father willing the Son’s (preincarnate) generation—hence the reference to an early creedal statement: “Light of Light.” In par 11, we have the Holy Spirit invoked as the one who expresses the Father’s will to the prophets. Lastly, in par 13 we have Jesus Christ called “the will.”
It would seem, as I inferred before, that there is some sort of conflation between the Son and the Spirit—but this may only be apparent due to translation or simply brevity in which the topic is being discussed. We have later indications that, similar to Augustine, Hippolytus perceived relational differences between the Persons:
And thus there appeared another beside Himself. But when I say another, I do not mean that there are two Gods, but that it is only as light of light, or as water from a fountain, or as a ray from the sun. For there is but one power, which is from the All; and the Father is the All, from whom comes this Power, the Word. (par 11)
We accordingly see the Word incarnate, and we know the Father by Him, and we believe in the Son, (and) we worship the Holy Spirit. (par 12)
The economy of harmony is led back to one God; for God is One. It is the Father who commands, and the Son who obeys, and the Holy Spirit who gives understanding: the Father who is above all, and the Son who is through all, and the Holy Spirit who is in all…For it is through this Trinity that the Father is glorified. For the Father willed, the Son did, the Spirit manifested. (par 14)
I shall not indeed speak of two Gods, but of one; of two Persons however, and of a third economy (disposition), viz., the grace of the Holy Ghost. For the Father indeed is One, but there are two Persons, because there is also the Son; and then there is the third, the Holy Spirit. (par 14)
This brings us to an interpretative juncture. We can view Hippolytus as theologically confused or we can discern that he was not viewing terms like “will” or “Spirit” as distinct categories of thought. It appears that “Spirit” can be either the “Holy Spirit” as a Person or a general reference to the immaterial essence of God (i.e. “God is Spirit,” John 4:24) “Will” appears to be a reference to the intentions of the Father, which are put into completion by the Son and made known by the Holy Spirit. Usually, it is the Holy Spirit which is identified at the Person in Whom we attribute the proverb “God is everywhere,” but to Hippolytus this appears to be the Son—at least for men via His incarnation. This is why the Son can be credited with actually working creation and doing the will of the Father, while the Spirit makes the Logos (who does these things) known. In this sense, it would seem that both the Son and Spirit are wills of the Father, but the willing of different things (doing and making apparent what was done.)
Concerning Christology, Hippolytus makes a reference to Jesus Christ being of “one mind of the Father,” implying a cooperative human will:
In the same manner the Son, who was sent and was not known of those who are in the world, confessed that He was in the Father in power and disposition. For the Son is the one mind of the Father. (par 7)
Hippolytus’ Biblicist approach appears to be rooted in his belief in the material sufficiency of Scriptures:
There is, brethren, one God, the knowledge of whom we gain from the Holy Scriptures, and from no other source. For just as a man, if he wishes to be skilled in the wisdom of this world, will find himself unable to get at it in any other way than by mastering the dogmas of philosophers, so all of us who wish to practise piety will be unable to learn its practice from any other quarter than the oracles of God. Whatever things, then, the Holy Scriptures declare, at these let us took. (par 9)
Hippolytus also makes the interesting observation the Jesus Christ’s humanity is enhypostasisized, something predating Cyril of Alexandria and subsequent Christological speculations:
Nor could the flesh subsist by itself apart from the Word, because it has its subsistence in the Word. (par 15)
Eternal origins of the Son vis a vis the Spirit are not speculated upon, as his concern seems to be about the incarnation:
Moreover, you are asking an account of the generation of the Word, whom God the Father in His good pleasure begot as He willed…Is it not enough for you to learn that the Son of God has been manifested to you for salvation if you believe, but do you also inquire curiously how He was begotten after the Spirit? No more than two [Gospels, Matthew and Luke], in truth, have been put in trust to give the account of His generation after the flesh; and are you then so bold as to seek the account (of His generation) after the Spirit, which the Father keeps with Himself, intending to reveal it then to the holy ones and those worthy of seeing His face? (par 16)
Jesus Christ took on the whole of humanity, but nothing specific is asserted as to what quality is flesh shared with fallen man, other than it was sinless:
Let us believe then, dear brethren, according to the tradition of the apostles, that God the Word came down from heaven, (and entered) into the holy Virgin Mary, in order that, taking the flesh from her, and assuming also a human, by which I mean a rational soul, and becoming thus all that man is with the exception of sin, He might save fallen man, and confer immortality on men who believe in His name. (par 17)
We may infer that the assumption of humanity was understood in a voluntarist sense, predating the Damascene. This is evidenced by Jesus Christ’s death as something that was not by necessity:
He who is inseparable from the Father cries to the Father, and commends to Him His spirit; and bowing His head, He gives up the ghost, who said, “I have power to lay down my life, and I have power to take it again;” and because He was not overmastered by death, as being Himself Life, He said this: “I lay it down of myself.” (par 18)