In the discussion of the Bible and its relation to the Trinity there is a particular term Trinitarians use which I think is misleading and that is “development.” The word and other related terms and ideas refer to the course of the historical development of the doctrine of the Holy Trinity from the 1st to the 4th centuries, the New Testament to the Nicene Creed.
As a point of historical fact, it is perfectly acceptable to say it developed because the doctrine did not appear out of thin air but there were a series of events that led to it. It is also correct to say that the path to the Trinity began with the New Testament (NT). The problem with the term development is how it is often used to suggest that given what the New Testament says, the formulation of Trinitarian doctrine was inevitable.
Trinitarian theologians will often say that in the NT there is no “developed” or “explicit” doctrine of the Trinity but will then assert that the “building blocks” or the “seeds” of the doctrine are found in it. Such language indicates by “development” they often mean more than a mere matter of history. They are talking about it the way a boy will develop into a man. I am certain they actually mean there was a trinitarian trajectory that was originally set by the NT because they call the NT “proto-Trinitarian”. Perhaps, you could say that proto-Trinitarian just means that it chronologically precedes the formulation of the Trinity. However, the problem is that term is often used interchangeably with “incipient Trinitarianism” which clearly means it was there in the text but had not yet fully emerged.
The reason why I am opposed to saying there was incipient Trinitarianism in the NT is because as far as I can tell there is no historical evidence to suggest that. As I discussed in The Missing Trinity, none of the particular vocabulary of later “developed” Trinitarian discourse appears in the NT. This is one of the major reasons why NT scholars know the text does not talk about the Trinity. The discourse about God, Jesus and the Spirit that we do find in the NT is conducted on completely different terms that fit their own 1st century Jewish milieu.
Most importantly, the reason why the NT is not proto-Trinitarian is that competing theologies all drew on the same group of texts, that, is the Bible. The reason that happened was because it was historically impossible for the Bible to be concerned with later theological debates. As I earlier said the NT was part of a different historical discussion conducted on very different terms. So all sides in later debates could appeal to it since there was nothing in it that definitively supported one position to the utter exclusion of another. NT scholar Stephen E. Fowl writes,
1The point is both pro- and anti-Nicene theologians made ready recourse to Paul. If one is to say that there are Trinitarian implications to Paul’s view of God, then one must say that there are Arian implications too.
I think this point can be expanded to included the entire Bible which both sides knowledgeably and fiercely debated. For most Trinitarian theologians the triune God was hidden in the Old Testament but revealed in the New so their case mostly rests on the NT. Now if one insists on calling the NT proto-Trinitarian, it could equally be called proto-Arian, proto-Modalist or pretty much proto- any historical doctrine involved in the debates surrounding the Trinity since they were all in differing ways trying to faithfully interpret the same text. To say in the NT the Trinity was “undeveloped”, not “explicit” or any such language is really a way of staking which side of the debate you are on. To call the NT proto-Trinitarian is really a pro-Nicene commitment and not an outright fact about what the NT writers were saying.
1Fowl S.E., “Paul and the Trinity”, p. 152, The Bible and Early Trinitarian Theology, eds. Christopher A. Beeley and Mark E. Weedman, Catholic University of America Press, 2018.