The Trinity doctrine is the result Christianity being born into a Greco-Roman world and 2nd - 4th century Christians using Greek/Neoplatonist philosophy to explain the Godhead. It can not be derived from the bible, but is accepted because of the creeds of the Catholic Church.
Quote:
2.2 The New Testament
The New Testament contains no explicit trinitarian doctrine. However, many Christian theologians, apologists, and philosophers hold that the doctrine can be inferred from what the New Testament does teach about God. But how may it be inferred? Is the inference deductive, or is it an inference to the best explanation? And is it based on what is implicitly taught there, or on what is merely assumed there? Many Christian theologians and apologists seem to hold it is a deductive inference.
In contrast, other Christians admit that their preferred doctrine of the Trinity not only (1) can't be inferred from the Bible alone, but also (2) that there's inadequate or no evidence for it there, and even (3) that what is taught in the Bible is incompatible with the doctrine. These Christians believe the doctrine solely on the authority of later doctrinal pronouncements of the True Christian Church (typically one of: the Catholic Church, the Eastern Orthodox tradition, or the mainstream of the Christian tradition, broadly understood). Some Catholic apologists have argued that this doctrine shows the necessity of the teaching authority of the Church, this doctrine being constitutive of Christianity but underivable from the Bible apart from the Church's guidance in interpreting it. This stance is not popular among Christians who are neither Catholic nor Eastern Orthodox. (2) would be the main sticking point, although some groups deny all three.
Many Christian apologists argue that the doctrine of the Trinity is “biblical” (i.e. either it is implicitly taught there, or it is the best explanation of what is taught there) using three sorts of arguments. They begin by claiming that the Father of Jesus Christ is the one true God taught in the Old Testament. They then argue that given what the Bible teaches about Christ and the Holy Spirit, they must be “fully divine” as well. Thus, we must, as it were, “move them within” the nature of the one God. Therefore, there are three fully divine persons “in God”. While this may be paradoxical, it is argued that this is what God has revealed to humankind through the Bible.
|
https://plato.stanford.edu/entries/t...ry.html#OneGod