Unitarians trace their history back to the Apostolic Age, i.e. the life of Jesus and the decades immediately after his death, and claim this doctrine was widespread during the pre-Nicene period, that is, before the First Council of Nicaea met in 325. Many believe their Christology (understanding of Jesus Christ) most closely reflects that of the “original Christians.” (For a discussion of the New Testament evidence, see Nontrinitarianism.)
While it is evident that other Christologies existed in the late 1st and early 2nd centuries, Jewish-Christian congregations tended to hold the view that Jesus was a great man and prophet, even the Son of God, but not God himself.
One of the earliest controversies over the nature of Christ that involved the propagation of “unitarian” ideas broke out at Rome during the episcopate of Victor I (189–199). This was the so-called “Monarchian controversy”, which originated in a revolt against the influential Logos theology of Justin Martyr and the apologists, who had spoken of Jesus as a second god. Such language was disturbing to some. Justin’s language appeared to promote ditheism (two gods). The view, however, was defended by Hippolytus of Rome, for whom it was essential to say that the Father and the Logos are two distinct “persons” (prosopa).
Some critics of Justin’s theology tried to preserve the unity of God by saying that there is no difference to be discerned between the ‘Son’ and the ‘Father’ (unless ‘Son’ is a name for the physical body or humanity of Christ and ‘Father’ a name for the divine Spirit within). This sort of thinking, known as Modal Monarchianism or Sabellianism, would one day lead to a compromise doctrine that the Father and the Son are consubstantial (of the same being).
Other critics preserved the unity of God by saying that Jesus was a man, but differentiated in being indwelt by the Spirit of God to an absolute and unique degree. They thus denied that Jesus was God or a god. They became known as “adoptionists”, because they suggested that Jesus was adopted by the Father to be his Son. This view was associated with Theodotus of Byzantium (the Shoemaker) and Artemon.
So even at this early stage we find evidence of proto-Arianism (Justin’s view) and proto-Socinianism (the Adoptionist view), though they were, as yet, not fully formed. Both of these theologies have similarities to latter day Unitarianism.
The Monarchian controversy came to a head again in the mid-3rd century. In 259 the help of Dionysius of Alexandria, was invoked in a dispute among the churches in Libya between adherents of Justin’s Logos-theology and some modalist Monarchians. Dionysius vehemently attacked the modalist standpoint.
He affirmed that the Son and the Father were as different as a boat and a boatman and denied that they were “of one substance” (homoousios). The Libyans appealed to Dionysius of Rome, whose rebuke to his Alexandrian namesake stressed the unity of God and condemned “those who divide the divine monarchy into three separate hypostases and three deities”.
Another crisis occurred over Paul of Samosata, who became bishop of Antioch in Syria in 260. Paul’s doctrine is akin to the primitive Jewish-Christian idea of the person of Christ and to the Christology of Theodotus of Byzantium (adoptionism). To many his doctrine seemed plain heresy, and a council of local bishops was held to consider his case in 268.
The bishops found it easier to condemn Paul than to expel him, and he remained in full possession of the church with his enthusiastic supporters. However, the bishops appealed to the Roman emperor, who decided that the legal right to the church building should be assigned “to those to whom the bishops of Italy and Rome should communicate in writing”. It was the first time that an ecclesiastical dispute had to be settled by the secular power. So Paul was put out of his church.
Arius, son of Ammonius, was a popular priest appointed presbyter for the district of Baucalis in Alexandria in 313. His views of the nature of Jesus, although not original, conflicted with the views held by Bishop Alexander of Alexandria.
Both Arius and Alexander held that Jesus was the Word (Logos) in human form; however, Arius held that the Word was a creation of God and had a beginning of existence, whereas Alexander held that the Word was co-eternal and consubstantial with God. When disagreement arose between the two men, forces were set in motion that resulted in the formation of the doctrine of the Trinity.
In the Nicene Creed adopted at the First Council of Nicaea in 325, wherein the Roman Emperor Constantine the Great got involved, the issue was considered settled and the adoption of Alexander’s view became the orthodox doctrine and all other views were considered heresy and officially suppressed. During the reign of the emperor Constantius II, however, the anti-Nicene party rose to prominence and exercised considerable control over the church for about a generation.
New creeds were drawn up to counter the homoousian doctrine of the Nicene Creed. When Theodosius I took the imperial throne, however, the tables were turned, and at the Council of Constantinople in 381, the position that the Father, the Son and the Holy Ghost were all the same being was agreed upon, and the formulation of the doctrine of the Trinity was complete. Theodosius outlawed all Nontrinitarian forms of Christianity.