Some where at or about 390 AD, Augustine wrote this concrening the "trinity."
They who have said that our Lord Jesus Christ is not God, or not very God, or not with the Father the One and only God, or not truly immortal because changeable, are proved wrong by the most plain and unanimous voice of divine testimonies; as, for instance, "In the beginning was the Word, and the Word was with God, and the Word was God." For it is plain that we are to take the Word of God to be the only Son of God, of whom it is afterwards said, "And the Word was made flesh, and dwelt among us," on account of that birth of His incarnation, which was wrought in time of the Virgin. But herein is declared, not only that He is God, but also that He is of the same substance with the Father; because, after saying, "And the Word was God," it is said also, "The same was in the beginning with God: all things were made by Him, and without Him was not anything made." Not simply "all things;" but only all things that were made, that is; the whole creature. From which it appears clearly, that He Himself was not made, by whom all things were made. And if He was not made, then He is not a creature; but if He is not a creature, then He is of the same substance with the Father. For all substance that is not God is creature; and all that is not creature is God. And if the Son is not of the same substance with the Father, then He is a substance that was made: and if He is a substance that was made, then all things were not made by Him; but "all things were made by Him," therefore He is of one and the same substance with the Father. And so He is not only God, but also very God. And the same John most expressly affirms this in his epistle: "For we know that the Son of God is come, and hath given usan understanding, that we may know the trueGod, and that we may be in His true Son Jesus Christ. This is the true God, and eternal life."
10. Hence also it follows by consequence, that the Apostle Paul did not say, "Who alone has immortality," of the Father merely; but of the One and only God, which is the Trinity itself. For that which is itself eternal life is not mortal according to any changeableness; and hence the Son of God, because "He is Eternal Life," is also Himself understood with the Father, where it is said, "Who only hath immortality." For we, too, are made partakers of this eternal life, and become, in our own measure, immortal. But the eternal life itself, of which we are made partakers, is one thing; we ourselves, who, by partaking of it, shall live eternally, are another. For if He had said, "Whom in His own time the Father will show, who is the blessed and only Potentate, the King of kings, and Lord of lords; who only hath immortality;" not even so would it be necessarily understood that the Son is excluded. For neither has the Son separated the Father from Himself, because He Himself, speaking elsewhere with the voice of wisdom (for He Himself is the Wisdom of God), says, "I alone compassed the circuit of heaven." And therefore so much the more is it not necessary that the words, "Who hath immortality," should be understood of the Father alone, omitting the Son; when they are said thus: "That thou keep this commandment without spot, unrebukeable, until the appearing of our Lord Jesus Christ: whom in His own time He will show, who is the blessed and only Potentate, the King of kings, and Lord of lords; who only hath immortality, dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom be honor and power everlasting. Amen." In which words neither is the Father specially named, nor the Son, nor the Holy Spirit; but the blessed and only Potentate, the King of kings, and Lord of lords; that is, the One and only and true God, the Trinity itself.
11. But perhaps what follows may interfere with this meaning; because it is said, "Whom no man hath seen, nor can see:" although this may also be taken as belonging to Christ according to His divinity, which the Jews did not see, who yet saw and crucified Him in the flesh; whereas His divinity can in no wise be seen by human sight, but is seen with that sight with which they who see are no longer men, but beyond men. Rightly, therefore, is God Himself, the Trinity, understood to be the "blessed and only Potentate," who "shows the coming of our Lord Jesus Christ in His own time." For the words, "Who only hath immortality," are said in the same way as it is said, "Who only doeth wondrous things." And I should be glad to know of whom they take these words to be said. If only of the Father, how then is that true which the Son Himself says, "For what things soever the Father doeth, these also doeth the Son likewise?" Is there any, among wonderful works, more wonderful than to raise up and quicken the dead? Yet the same Son saith, "As the Father raiseth up the dead, and quickeneth them, even so the Son quickeneth whom He will." How, then, does the Father alone "do wondrous things," when these words allow us to understand neither the Father only, nor the Son only, but assuredly the one only true God, that is, the Father, and the Son, and the Holy Spirit?
12. Also, when the same apostle says, "But to us there is but one God, the Father, of whom are all things, and we in Him; and one Lord Jesus Christ, by whom are all things, and we by Him," who can doubt that he speaks of all things which are created; as does John, when he says, "All things were made by Him"? I ask, therefore, of whom he speaks in another place: "For of Him, and through Him, and in Him, are all things: to whom be glory for ever. Amen." For if of the Father, and the Son, and the Holy Spirit, so as to assign each clause severally to each person: of Him, that is to say, of the Father; through Him, that is to say, through the Son; in Him, that is to say, in the Holy Spirit,-it is manifest that the Father, and the Son, and the Holy Spirit is one God, inasmuch as the words continue in the singular number, "To whom be glory for ever." For at the beginning of the passage he does not say, "O the depth of the riches both of the wisdom and knowledge" of the Father, or of the Son, or of the Holy Spirit, but "of the wisdom and knowledge of God!" "How unsearchable are His judgments, and His ways past finding out! For who hath known the mind of the Lord? or who hath been His counsellor? Or who hath first given to Him and it shall be recompensed unto him again? For of Him, and through Him, and in Him, are all things: to whom be glory for ever. Amen." But if they will have this to be understood only of the Father, then in what way are all things by the Father, as is said here; and all things by the Son, as where it is said to the Corinthians, "And one Lord Jesus Christ, by whom are all things," and as in the Gospel of John, "All things were made by Him?" For if some things were made by the Father, and some by the Son, then all things were not made by the Father, nor all things by the Son; but if all things were made by the Father, and all things by the Son, then the same things were made by the Father and by the Son. The Son, therefore, is equal with the Father, and the working of the Father and the Son is indivisible. Because if the Father made even the Son, whom certainly the Son Himself did not make, then all things were not made by the Son; but all things were made by the Son: therefore He Himself was not made, that with the Father He might make all things that were made. And the apostle has not refrained from using the very word itself, but has said most expressly, "Who, being in the form of God, thought it not robbery to be equal with God;" using here the name of God specially of the Father; as elsewhere, "But the head of Christ is God."
13. Similar evidence has been collected also concerning the Holy Spirit, of which those who have discussed the subject before ourselves have most fully availed themselves, that He too is God, and not a creature. But if not a creature, then not only God (for men likewise are called gods ), but also very God; and therefore absolutely equal with the Father and the Son, and in the unity of the Trinity consubstantial and co-eternal. But that the Holy Spirit is not a creature is made quite plain by that passage above all others, where we are commanded not to serve the creature, but the Creator; not in the sense in which we are commanded to "serve" one another by love, which is in Greek douleuein, but in that in which God alone is served, which is in Greek latreuein. From whence they are called idolaters who tender that service to images which is due to God. For it is this service concerning which it is said, "Thou shalt worship the Lord thy God, and Him only shalt thou serve." For this is found also more distinctly in the Greek Scriptures, which have latreuseij. Now if we are forbidden to serve the creature with such a service, seeing that it is written, "Thou shalt worship the Lord thy God, and Him only shalt thou serve" (and hence, too, the apostle repudiates those who worship and serve the creature more than the Creator), then assuredly the Holy Spirit is not a creature, to whom such a service is paid by all the saints; as says the apostle, "For we are the circumcision, which serve the Spirit of God," which is in the Greek latreuontej. For even most Latin copies also have it thus, "We who serve the Spirit of God;" but all Greek ones, or almost all, have it so. Although in some Latin copies we find, not "We worship the Spirit of God," but, "We worship God in the Spirit." But let those who err in this case, and refuse to give up to the more weighty authority, tell us whether they find this text also varied in the mss.: "Know ye not that your body is the temple of the Holy Ghost, which is in you, which ye have of God?" Yet what can be more senseless or more profane, than that any one should dare to say that the members of Christ are the temple of one who, in their opinion, is a creature inferior to Christ? For the apostle says in another place, "Your bodies are members of Christ." But if the members of Christ are also the temple of the Holy Spirit, then the Holy Spirit is not a creature; because we must needs owe to Him, of whom our body is the temple, that service wherewith God only is to be served, which in Greek is called latreia. And accordingly the apostle says, "Therefore glorify God in your body."
- On the Trinity;
Chapter 6.-That the Son is Very God, of the Same Substance with the Father. Not Only the Father, But the Trinity, is Affirmed to Be Immortal. All Things are Not from the Father Alone, But Also from the Son. That the Holy Spirit is Very God, Equal with the Father and the Son.
While I don't agree with everything he taught, just like a stopped clock is right twice a day, Augustine did get this right.