Ignatius of Antioch:
Study, therefore, to be established in the doctrines of the Lord and the apostles, that so all things, whatsoever ye do, may prosper both in the flesh and spirit; in faith and love; in the Son, and in the Father, and in the Spirit; in the beginning and in the end; with your most admirable bishop, and the well-compacted spiritual crown of your presbytery, and the deacons who are according to God. Be ye subject to the bishop, and to one another, as Jesus Christ to the Father, according to the flesh, and the apostles to Christ, and to the Father, and to the Spirit; that so there may be a union both fleshly and spiritual. —
Epistle to the Magnesians, Chapter 13 [SR]
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After the foregoing instructions, baptize in the name of the Father, and of the Son, and of the Holy Spirit, in living [running] water…. If you have neither, pour water three times on the head, in the name of the Father, and of the Son, and of the Holy Spirit. —
Didache 7:1
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For this cause, yea and for all things, I praise Thee, I bless Thee, I glorify Thee, through the eternal and heavenly High-priest, Jesus Christ, Thy beloved Son, through whom with Him and the Holy Spirit be glory both now [and ever] and for the ages to come. Amen. —
Martyrdom of Polycarp 14:3
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Theophilus of Antioch:
...the three days before the luminaries were created are types of the Trinity, God, his Word, and his Wisdom. —
To Autolycus 2:15
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Tertullian:
And at the same time the mystery of the
oikonomia is safeguarded, for the unity is distributed in a Trinity. Placed in order, the three are the Father, Son, and Spirit. They are three, however, not in condition, but in degree; not in being, but in form; not in power, but in kind; of one being, however, and one condition and one power, because he is one God of whom degrees and forms and kinds are taken into account in the name of the Father, and of the Son, and of the Holy Spirit. —
Against Praxeas 2
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Hippolytus:
The Father's Word, therefore, knowing the economy and the will of the Father, to wit, that the Father seeks to be worshipped in none other way than this, gave this charge to the disciples after he rose from the dead: "Go ye and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost." (Matt 28:19) And by this he showed that whosoever omitted any one of these, failed in glorifying God perfectly. For it is through the Trinity that the Father is glorified. For the Father willed, the Son did and the Spirit manifested. —
Against Noetus
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Origen:
For it is the Trinity alone which exceeds every sense in which not only temporal but even eternal may be understood. It is all other things, indeed, which are outside the Trinity, which are to be measured by time and ages.... It seems right to inquire into the reason why he who is 'born again through God' to salvation has need of both Father and Son and Holy Spirit and will not obtain salvation apart from the entire Trinity, and why it is impossible to become partaker of the Father or the Son without the Holy Spirit. In discussing these points it will undoubtedly be necessary to describe the activity which is peculiar to the Holy Spirit and that which is peculiar to the Father and Son.
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Novatian:
For Scripture as much announces Christ as also God, as it announces God himself as man. It has as much described Jesus Christ to be man, as moreover it has also described Christ the Lord to be God. Because it does not set forth him to be the Son of God only, but also the son of man; nor does it only say, the son of man, but it has also been accustomed to speak of him as the Son of God. So that being of both, he is both, lest if he should be one only, he could not be the other. For as nature itself has prescribed that he must be believed to be a man who is of man, so the same nature prescribes also that he must be believed to be God who is of God…. Let them, therefore, who read that Jesus Christ the son of man is man, read also that this same Jesus is called also God and the Son of God. —
Treatise on the Trinity
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Dionysius:
Next, I may reasonably turn to those who divide and cut to pieces and destroy that most sacred doctrine of the Church of God, the Divine Monarchy, making it as it were three powers and partive subsistences and godheads. I am told that some among you who are catechists and teachers of the Divine Word, take the lead in this tenet, who are diametrically opposed, so to speak, to Sabellius' opininons; for he blasphemously says that the Son is the Father, and Father the Son, but they in some sort preach three Gods, as dividing the sacred Unity into three subsistences foreign to each other and utterly separate. For it must be that with the God of the Universe, the Divine Word is united, and the Holy Ghost must repose and habitate in God; thus in one as in a summit, I mean the God of the Universe, must the Divine Trinity be gathered up and brought together....Neither, then, may we divide into three godheads the wonderful and divine Unity...Rather, we must believe in God, the Father Almighty; and in Christ Jesus, his Son; and in the Holy Spirit; and that the Word is united to the God of the universe. 'For,' he says, 'The Father and I are one,' and 'I am in the Father, and the Father in me'. For thus both the Divine Trinity and the holy preaching of the Monarchy will be preserved. —'De decretis Nic. syn.
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I have no clue where you’re pulling this 500 years from. Here are several ECF’s positing clear unmistakable Trinitarian language. But keep right on going headlong into John 8:24 if you must.
