Anti-Trinitarian groups such as Muslims, Oneness Pentecostals, and Jehovah’s Witnesses frequently launch the assertion that doctrine of the Trinity was conceived in the 4th century (viz. at the Council of Nicaea, A.D. 325). Utterly, controlled by their unitarian assumption that God is one person, not revealed in three persons, they reject the notion that God is triune, however there are two major flaws to their uniformed assertions:
- In that era, historically, there was no “supreme” popish Roman Catholic Church as it appears from the 13th century onwards. Thus, back in the 4th century, there was only a church in Rome as there was a church in Alexandria, Antioch, Constantinople, Smyrna, Philippi, etc. In fact, all the early churches were “catholic” in the sense of belonging to the “universal church”.
- The Trinity was not the issue at Nicaea. Rather, due to the assertions of the heretic Arius (around A.D. 318) that the Son was not God by nature, the council addressed the issue of the Son’s ontological (nature) relationship to the Father. Basically was the Son homoousios (of the “same substance” as God) or heteroousios (of a “different substance,” created). Years before, the church had already proclaimed and established the concept of the Trinity. Again, that was not the issue at Nicaea. In point of fact, none of the written documents that came out of Nicaea by men that were there, contained either the word “Trinity” or even a direct reference to it.
The Concept of the Trinity
The doctrine of the Trinity did not originate from the early church, rather it was established in the content of divine revelation of both the OT and NT.
For example, in the OT, we find plural words being applied to the one God (cf. Gen. 1:26; 3:22; 11:7; Eccl. 12:1; Isa. 6:3, 8; 54:5 et al.). In Isa. 9:6, the Messiah is identified as El gibbor (“mighty God”). In Dan. 7:9-14, we find two objects of divine worship is presented—the Ancient of Days and the Son of Man. Further, there are many Angel of the Lord appearances (preincarnate Christ), such as to Hager (cf. Gen. 16:11-13); Abraham (cf. Gen. chaps. 18-19); Moses (cf. Exod. 3:1ff.); Gideon (cf. Judg. 6:11-24); Manoah (cf. Judg. 13:16, 21) et al. The angel of the Lord was not a created, indefinite angel. He was identified as God/YHWH and claimed He was the “the God of Abraham, the God of Isaac, and the God of Jacob” (Exod. 3:6)—YHWH, yet a distinct person from another YHWH (cf. Gen. 19:24). For more information on the angel of the Lord see The Preincarnate Christ as the Angel of the Lord
The NT contains many passages that clearly present the concept of the Trinity—cf. Matt. 28:19; John 1:1, 3, 18; 5:17-18; 14:23; 17:5; 20:28; Rom. 15:30; 2 Cor. 13:14; 4:4-6; Eph. 2:18; 2 Thess. 2:13; Titus 3:5-7; Heb. 1:1-12; 1 Pet. 1:2-3; 1 John 1:1-3; Rev. 5:13-14 and many more could be cited.
Debunking the Unitarian Belief
The concept of the Trinity has been well established by the early church immediately following the apostolic age and certainly not an invention of the non-existent Roman Catholic Church. The concept starts in Genesis and is fully revealed in the NT. Patristic and early church authority J. D. Kelly observes:
The reader should notice how deeply the conception of a plurality of divine Persons was imprinted in the apostolic tradition and the popular faith. Though as yet uncanonized, the New Testament was already exerting a powerful influence; it is a commonplace that the outlines of a dyadic and a triadic pattern are clearly visible in its pages.
Below is a very partial list of early pre-fourth century examples of a variety of early church Fathers expressing the concept of the Trinity. Also see The Trinity and the Early Church: Debunking the Oneness Unitarian Mythfor a fuller list of citations.
Didachē (viz. “The Teachings of the Twelve Apostles”; c. A.D. 70): “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” (7.1).
Ignatius Bishop of Antioch (c. A.D. 107): “There is one Physician who is possessed both of flesh and spirit; both made and not made [agennētos, “unoriginate, eternal”]; God existing in flesh; true life in death; both of Mary and of God; first possible and then impossible, even Jesus Christ our Lord (Letter to the Ephesians, 7).
“Jesus Christ, who was with the Father [para patri] before the beginning of time [pro aiōnōn], and in the end was revealed…. He, being begotten by the Father before the beginning of time, was God the Word, the only-begotten Son, and remains the same for ever….” (Letter to the Magnesians, 6). Note the linguistic parallel with John 17:5—where the same preposition denoting the Son’s eternality is used (here- pro aiōnōn, “before time,” John 17:5- pro tou ton kosmon einai, “before the world was”) and the same preposition followed by dative case expressing a distinction between persons (here- para patri, “with the Father,” John 17:5- para seautō, “together with Yourself,” para soi, “with You.”
“For our God, Jesus Christ, now that He is with the Father, is all the more revealed [in His glory]. Christianity is not a thing of silence only, but also of [manifest] greatness (Letter to the Romans, 3).
Polycarp Bishop of Smyrna (c. A.D. 130-150): [in his last prayer before his martyrdom] “O Lord God Almighty, the Father of thy beloved and blessed Son Jesus Christ…. I bless Thee, I glorify Thee, along with the everlasting and heavenly Jesus Christ, Thy beloved Son, with whom, to Thee, and the Holy Spirit, be glory both now and to all coming ages. Amen” (Martyrdom of Polycarp, 14).
Justin Martyr (c. A.D. 160): “’Let Us make,’ –I shall quote again the words narrated by Moses himself, from which we can indisputably learn that [God] conversed with someone who was numerically distinct from Himself, and also a rational Being….” (Dialogue with Trypho, 62).
Athenagoras of Athens (c. A.D. 175): “Who, then, would not be astonished to hear men who speak of God the Father, and of God the Son, and of the Holy Spirit, and who declare both their power in union and their distinction in order, called atheists?…. For, as we acknowledge a God, and a Son his Logos, and a Holy Spirit, united in essence, – the Father, the Son, the Spirit….” (A Plea for Christians, 10, 24).
Theophilus Bishop of Antioch (c. A.D. 180): “In like manner also the three days which were before the luminaries, are types of the Trinity of God, and His Word, and His wisdom” (To Autolycus, 2.15).
Irenaeus Bishop of Lugdunum (now Lyon; c. A.D. 180): “For with Him were always present the Word and Wisdom, even the Son and the Spirit, by whom and in whom, freely and spontaneously, He made all things, to whom also He speaks, saying, “Let Us make man after Our image and likeness…. that the Word, namely the Son, was always with the Father; and that Wisdom also, which is the Spirit, was present with Him, anterior to all creation….” (Against Heresies, 4.20.1, 3).
“[the church believes] in one God, the Father Almighty, Maker of heaven, and earth … and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit….” (ibid., 1.10.1).
Clement of Alexandria (c. A.D. 190): “I understand nothing else than the Holy Trinity to be meant; for the third is the Holy Spirit, and the Son is the second, by whom all things were made according to the will of the Father” (Stromata, Book V, Ch. 14)
Hippolytus (c. A.D. 205): “Beside Him there was nothing; but He, while existing alone, yet existed in plurality (Against Noetus, 10; Gk. monos ōn polus ēn, lit., “alone existing [yet] plurality/many was.”
Tertullian (c. A.D. 213): “He commands them to baptize into the Father and the Son and the Holy Ghost, not into a unipersonal God. And indeed it is not once only, but three times, that we are immersed into the Three Persons, at each several mention of Their names” (Against Praxeas, 26).
Novatian the Roman Presbyter (c. A.D. 256): “it is declared [Gen. 19:24]: ‘Then the Lord [YHWH] rained upon Sodom and upon Gomorrah fire and brimstone from the Lord [YHWH] out of heaven.’ But although the Father, being invisible.… But this the Son of God, “The Lord rained from the Lord upon Sodom and Gomorrah brimstone and fire.” And this is the Word of God. And the Word of God was made flesh, and dwelt among us; and this is Christ. It was not the Father, then, who was a guest with Abraham, but Christ. Nor was it the Father who was seen then, but the Son…. Rightly, therefore, Christ is both Lord and God (“De Trinitate,” in Treatise of Novatian Concerning the Trinity, 18).
Dionysius, Bishop of Alexandria (c. A.D. 262): “The Son alone, always co-existing with the Father…. For on this account after the Unity there is also the most divine Trinity….” (Works of Dionysius, Extant Fragments).
Gregory Thaumaturgus the Wonder-worker (c. A.D. 260): “There is a perfect Trinity, in glory and eternity and sovereignty, neither divided nor estranged. Wherefore there is nothing either created or in servitude in the Trinity…. And thus, neither was the Son ever wanting to the Father, nor the Spirit to the Son; but without variation and without change, the same Trinity abides ever (A Declaration of Faith).
Methodius of Olympus (c. A.D. 305): “For the kingdom of the Father, of the Son, and of the Holy Ghost, is one, even as their substance is one and their dominion one…. we worship the one Deity in three Persons, subsisting without beginning, uncreated, without end, and to which there is no successor…. For nothing of the Trinity will suffer diminution, either in respect of eternity, or of communion, or of sovereignty (Oration on the Psalms, 5).
“but also the glory to be adored by all of that one of the sacred Trinity…. They say: “The whole earth is full of His glory.” For we believe that, together with the Son, who was made man for our sakes, according to the good pleasure of His will, was also present the Father, who is inseparable from Him as to His divine nature, and also the Spirit, who is of one and the same essence with Him (Oration concerning Simon and Anna on the Day that they met in the Temple, 2).
Many more citations can be presented that undeniably show within the proper context of the writers aforementioned, that the early church prior to Nicaea (325) unitedly embraced the concept of the Trinity and rejected Oneness-unitarianism in all forms. They saw and taught that the one true God was triune—God the Father, God the Son, and God the Holy Spirit—three distinct coequal, coeternal, and coexistent persons, which was the Faith of the OT believers and the NT church.
 In Isaiah 10:21, the same description (El gibbor) is applied to YHWH (cf. also Deut. 10:17).
 J. D. Kelly, Early Christian Doctrines (San Francisco, CA: HarperCollins, 1978, 88.