Below are significant comments to a question posted at BSA in October 2025. The extracts pasted below are in the same order as the overall post at BSA. All emphasis is mine.
Original Question summarized: Why the trinity at all? Why not a duality: The Father and Son? Why did Christians find it necessary to name the Holy Spirit an entity or being?
See Bart’s Post – How Did the Holy Spirit Get Into the Trinity? In the Beginning…. May 5, 2021
Charles Bledsoe [Provided the link to Bart’s post, then summarized what Bart said as follows.] The Bart Ehrman Blog post that I posted a link to above gives a plausible explanation of the inclusion of the Holy Spirit in the multi-personality of the Christian deity. Essentially, it was largely the result of the incorrect takeaway of early Christians from the Greek Septuagint’s faulty translation of Genesis 1:1 and 1:2. It uses the Greek word pneuma to translate the Hebrew ruah, which is okay, since ruah, and pneuma both mean breath or wind. But there was a little problem with pneuma that had big theological consequences down the line. Because of the association of breath with life, pneuma (and also ruah) had also come to mean spirit. And what’s more, the erring Septuagint translation of the opening verses of Genesis gave early Christian readers to read them as saying that God’s pneuma (Spirit) as a distinct entitative aspect of God played a part in creation. This helped to get them thinking in terms of a Spirit that’s an individual member of an intra-divine plurality of the deity. And of course early Christians already being in the mode of attributing multi-personality to God—thanks to their divinization of Christ and the need to reconcile that with monotheism—played a significant part in their expansion of God’s internal multiplicity from a duality into a Trinity. It sealed the theological deal. Thus and so, Christian theology ended up with a Trinitarian conception of God that includes a Holy Spirit that started out as a wind from God, and subsequently became reified into a distinct aspect of the Godhead, and then was turned into an individual person of a triune deity. In short, the Holy Spirit is the result of the long, strange trip of the Hebrew and Greek words and concepts of ruah and pneuma.
Schaun Wheeler – Trinitarianism feels so settled now, but for the first few centuries it was one of several competing ideas. The folks who pushed for “one God in three persons” ended up with imperial backing, so their view stuck – not necessarily because they had the stronger theology, but because they won the political fight. It’s easy to look back and think the Trinity was the obvious conclusion, but it really wasn’t. Even later on, there were movements like the 19th-century Church of God Binitarians who only recognized Father and Son, and today the Church of Jesus Christ of Latter-day Saints still rejects the “one substance” idea. Orthodoxy is precariously contingent. A different emperor, a lost manuscript, or one council going the other way, and the map of “established doctrine” would look completely different. Orthodoxy endures not because it was inevitable, but because history hardened around it – every settled doctrine is a fossil of an argument someone once barely won.
Michael Waddell – It’s an odd journey. Let’s start with the unity of God.
God is one, we all agree. At least, that’s how it starts. But God created the world with his Word (logos if you’re Greek), right? That Word was with God from the beginning, so of course this Word would be divine. So God is one, but he’s two. And his Spirit (pneuma) was there too, so we hypostasize that as a divine entity as well. We’re up to three. But what about the Mind (nous) of God? Is that less divine than his Word? How about the Love (agape) of God, or the Wisdom (sophia) of God, or the Glory (doxa) of God? This “trinity” is feeling a bit crowded. What is it now, a heptinity? And hey, didn’t John say that his followers became children of God and received the same glory he had? In fact, he prayed that his followers would become “One” in the same way he was “One” with the Father. If we accept Jesus as divine, shouldn’t all believers be in that “trinity” with him? In my opinion, that tri- prefix is far too small. Let’s swap it out for a uni- prefix…and hey, look! We’re back at the unity of God.
In reality, the doctrine of the Trinity, like all credal doctrines, was specified in order to exclude certain Christians deemed “heretics”. Athanasius didn’t hate Arius because it was so noxious to believe that God created his Word — he hated Arius because they were personal rivals for the Bishopric of Alexandria, and Arius had a large and loyal following. After Arius publicly denounced a particularly poorly-worded speech by Athanasius, Athanasius pulled out all the stops to get Arius’ views discredited, and at the Council of Nicaea, they were. The mandatory acceptance of the doctrine of the Trinity evolved out of that interpersonal dispute.
Mark Potratz – I can’t help but think that Christian apologists, like Tertullian are writing against what they see as heretical ideas. References to the Holy Spirit are all though out the canonical Gospels. I think that the apologists needed to develop an orthodox way of perceiving the Holy Spirit in relation with Christ and God so that they could stand on a solid foundation against what they considered heretical.
Charles Bledsoe – Mark Potratz. Good point. The development of orthodox Christian theology in the Patristic period was to some degree conflict-driven, a reactive development, a dynamic, dialectical (not in a Hegelian sense) process of engaging with opposing theological ideas that were considered heretical and working out a formulation of doctrine that took account of them, that resolved conflict with them. The doctrine of the Trinity emerged from this process, from oppositional engagement with competing Christologies, and the inclusion of the Holy Spirit in the multi-personality of God also received some of its impetus from the same dynamic.
