The grace of the Lord Jesus Christ, and the love of God, and the fellowship of the Holy Spirit be with you all (2 Cor. 13:14).
Virtually all non-Christian cults (esp. Oneness believers and Jehovah’s Witnesses) reject the doctrine of the Trinity and teach that the early church had no such concept of a triune God, but rather they held to a unitarian concept of God (i.e., God existing as one Person). Because of a great lack of study in the area of Patristics (i.e., church Fathers), these groups normally assert that the origins of the doctrine of the Trinity first emerged at the Council of Nicea in A.D. 325.
So vast is the evidence that the early church envisaged a tri-personal God and not a unitarian or unipersonal deity to which groups such as Oneness Pentecostals (as well as Muslims, Jews, and JWs) hold, that Oneness writers such as William B. Chalfant make desperate attempts to convince Oneness believes that the early church Fathers were really modalists (Oneness):
the trinity doctrine exists only on paper. . . . No apostle of our Lord Jesus Christ ever taught such a doctrine. . . . None of the immediate disciples of the apostles (e.g., Clement Ignatius, Hermas, or Polycarp) taught such a doctrine . . . Trinities Abound in the ancient, false religions. . . .
With no historic justification, Chalfant (and others Oneness writers) conveniently assumes his conclusion that is meant to be proved, namely—that the early church Fathers were modalists! What I find interesting is that nearly every non-Christian cult uses this same line of reasoning, which is nothing more that patent historical revisionism.
It is not surprising that the greatest and most authoritative Christian theologians and church historians objectively disagree with the Oneness historical assumption that the early Christians in the days immediately following the apostolic age were Oneness. Despite the fact that many church Fathers utilized first person plural references in the OT (“Our,” “Us”; cf. Gen. 1:26; 3:22; 11:7; Isa. 6:8) to substantiate that God was multi-personal, it was the Trinitarian baptismal formula (cf. Matt. 28:19) that was used and quoted by many early church Fathers to show that God was Triune. The evidence clearly shows that the early church conceptualized a distinction of Persons in the Godhead—they were not Oneness.
Some of the earliest writings that have come down to us are those that belong to the category of the “apostolic Fathers.” Many of these men were actual disciples the original apostles and leaders of the original churches. The few citations below (there are massive amounts!) plainly indicate their view of a triune God.
The Epistle of Barnabas (c. A.D. 70):
Probably not written by the biblical character Barnabas, but whoever the author was the Epistle of Barnabas was written very early when some of the original apostles were still alive. Notice how the plural verb “Let Us make” in Genesis 1:26 is used differentiating God the Father from Jesus:
And further, my brethren, if the Lord [Jesus] endured to suffer for our soul, he being the Lord of all the world, to whom God [the Father] said at the foundation of the world, ‘Let us make man after our image, and after our likeness,’ understand how it was that he endured to suffer at the hand of men (Epistle of Barnabas, 5).
Clement bishop of Rome (c. A.D. 96):
Clement of Rome wrote an epistle to the original Corinthian church. He was perhaps the same Clement who was Paul’s close companion mentioned in Philippians 4:3. In Clement’s salutation, he clearly distinguishes the Father from the Lord Jesus Christ:
The Church of God which sojourns at Rome, to the Church of God sojourning at Corinth, to those who are called and sanctified by the will of God, through our Lord Jesus Christ: Grace to you, and peace, from Almighty God through Jesus Christ, be multiplied (Letter to the Corinthians, 1).
Surely if Jesus as the Father (the Oneness view) was the “apostolic doctrine,” as Oneness teachers would like us to believe, why was Clement, who was perhaps Paul’s associate, clearly distinguishing the Father from the Lord Jesus Christ? Clement then refers to a very Trinitarian passage (Eph. 4:4-6):
Let us cleave, therefore, to the innocent and righteous, since these are the elect of God. Why are there strifes, and tumults, and divisions, and schisms, and wars among you? Have we not [all] one God and one Christ? Is there not one Spirit of grace poured out upon us? (emphasis added; ibid., 46).
Ignatius bishop of Antioch (c. A.D. 107):
Ignatius, bishop of the church at Antioch, was another apostolic church Father. What he says should be considered; after all, he was a leader of the original church at Antioch:
There is one Physician who is possessed both of flesh and spirit; both made and not made; 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).
Clearly, Ignatius does not see the Father and the Son as the same Person. In the same letter, he distinguishes the Father from the Son and the Holy Spirit:
as being stones of the temple of the Father, prepared for the building of God the Father, and drawn up on high by the instrument of Jesus Christ, which is the cross, making use of the Holy Spirit as a rope, while your faith was the means by which you ascended, and your love the way which led up to God (emphasis added; ibid., 9).
Even more descriptive, Ignatius, in his letter to the Magnesians, speaks of Jesus being with the Father before time:
Jesus Christ, who was with the Father before the beginning of time, 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. . . . (emphasis added; Letter to the Magnesians, 6).
That Ignatius calls Jesus “the only-begotten Son,” and that He (the Son) was “God the Word,” goes straight against Oneness theology, which says that the Son had His beginning in Bethlehem. In his letter to the Roman church, he explicitly distinguishes the Father from the Son:
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).
In the introduction to his letter to the Romans, please notice the specific language Ignatius uses to clearly differentiate the Father from Jesus, “the Son of the Father”:
Ignatius, who is also called Theophorus [“God-inspired”], to the Church which has obtained mercy, through the majesty of the Most High Father, and Jesus Christ, His only-begotten Son; the Church which is beloved and enlightened by the will of Him that willeth all things which are according to the love of Jesus Christ our God, which also presides in the place of the report of the Romans, worthy of God, worthy of honour . . . and which presides over love, is named from Christ, and from the Father, which I also salute in the name of Jesus Christ, the Son of the Father. . . . (emphasis added).
John 17:5 and The Letter to the Magnesians
What is also noteworthy is the striking parallel in Ignatius’s letter to the Magnesians (c. A.D. 107) with John 17:5. Ignatius states: “Jesus Christ, who ‘before the ages’ [pro aiōnōn] was ‘with the Father’ [para patri] and appeared at the end of time” (chap. 6).
Specifically, both John and Ignatius use para with the dative denoting a marked distinction between Jesus and the Father and both use the preposition pro (“before”) to indicate that their distinction existed from eternity—“before time.”
Thus, Ignatius following the apostolic tradition envisages Jesus Christ as being para (“with/in the presence of”) the Father— pro aiōnōn (“before time”)—, which again is consistent with Trinitarianism, not Oneness unitarianism.
Hermas (c. A.D. 120):
Hermas was perhaps the same Hermas to whom Paul sends his greetings in Romans 16:14 around A.D. 57. In The Shepherd, Hermas writes in clear contradiction to the Oneness doctrine of the non-eternal Son:
The Son of God is older than all his creation, so that he became the Father’s adviser in his creation. Therefore, also he is ancient (The Shepherd, Ninth Similitude, 12).
Polycarp bishop of Smyrna (c. A.D. 130-150):
The beloved Polycarp, bishop of Smyrna, who claimed he had been a “Christian for eighty-six years,” was also, according to Irenaeus and Eusebius, a disciple of the Apostle John. In his last prayer before he was martyred, Polycarp glorifies the triune God:
O Lord God Almighty, the Father of thy beloved and blessed Son Jesus Christ, by whom we have received the knowledge of Thee . . . I give Thee thanks that Thou hast counted me, worthy of this day and this hour, that I should have a part in the number of Thy martyrs, in the cup of thy Christ, to the resurrection of eternal life, both of soul and body, through the incorruption [imparted] by the Holy Ghost. . . . Wherefore also I praise Thee for all things, 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 (emphasis added; Martyrdom of Polycarp, 14).
Mathetes (c. A.D. 130):
In his letter to Diognetus, Mathetes, who claimed, “having been a disciple of the apostles,” speaks clearly of the eternality of the Word, not as the Father, but as being sent from the Father:
For which reason He [the Father] sent the Word, that He might be manifested to the world. . . . This is He who was from the beginning, who appeared as if new, and was found old, and yet who is ever born afresh in the hearts of the saints. This is He who, being from everlasting, is today called the Son. . . . (emphasis added; Letter to Diognetus, 11).
Aside from the many subsequent church Fathers that passionately affirmed and defended the Trinity (e.g., Athenagoras, Theophilus, Irenaeus, Hippolytus, Tertullian, Athanasius, Cyril, etc.), the “apostolic Fathers” clearly envisaged a tri-personal God. Recognized Patristic authority and early church historian, J. N. D. Kelly, gives these observations:
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 out-lines of a dyadic and a triadic pattern are clearly visible in its pages.
There are many more citations that can be presented. The point is Oneness teachers attempt to revise history in order to make the early church Oneness. I would challenge anyone to do an honest study of the early church reading recognized church history and Patristic scholars, and objectively evaluating the early church Fathers as to what they actually said and taught in context.
 Note that the repetition of the Greek article (tou, “the”) and the conjunction (kai, “and”) in this passage: lit., “of the [tou] Lord Jesus Christ . . . and [kai] . . . of the [tou] God and [kai] . . . of the [tou] Holy Spirit. . . .” Grammatically, this construction (viz. Granville Sharp’s Greek rule #6) indicates a distinction of persons. Same with Matt. 28:19: lit., “in the name of the [tou] Father and of the [kai tou] Son and of the [kai tou] Holy Spirit.”
 Chalfant, Ancient Champions of Oneness, 116-18. He speaks this way in most of his writings that deal with church history, as do most Oneness teachers.
 E.g., Eusebius, Socrates, Lightfoot, Schaff, Kelly, Bruce, Beckwith, etc.
 Kelly, Early Christian Doctrines, 88.