Charles Freeman explains why AD 381 was a defining moment in the history of European thought.
The doctrine of the Trinity – that God the Father, Jesus the begotten Son of God, and the Holy Spirit are equal but distinct members of a single Godhead – is an article of faith that lies at the core of Christian belief. As the Catechism of the Catholic Church puts it, it is a mystery hidden by God, inaccessible by reason alone, and only known because God has revealed it. So should historians, as well as theologians, be concerned with it? I believe there are good reasons why we should.
So the historian has to ask how this particular doctrine ever became embedded at the centre of Christian thought. For some there was no problem. Pope Gregory the Great (r.590–604), for instance, claimed that the Trinity had always been known, although he had to accept that the patriarchs of the Old Testament had rarely preached on the issue. Yet, while it is clear that the scriptures do refer independently to God the Father, his ‘son’ Jesus, and a Holy Spirit, there is virtually no mention of them as a Trinity, even in the New Testament. The only verses that place the three figures together come in Matthew 28:19 (‘Go forth and ... baptize men everywhere in the name of the Father and the Son and the Holy Spirit’) and the conclusion of Paul’s Second Letter to the Corinthians; and neither of them describes any relationship between them. In fact, a straightforward reading of the New Testament suggests that Jesus is almost always presented as subordinate to ‘the Father’, and this seems to have been the approach taken by the early Church.