A Brief Explanation of the Trinity - Doesn’t this doctrine really come from later Church fathers?
This doctrine is developed by great theologians like Athanasius (c. AD 296-373) and Augustine (AD 354-430), but it was not invented by them. The New Testament was written to clarify pressing doctrinal and pastoral problems and issues that arose in the church. Here are four examples: what did Jesus teach or do about sickness or dietary laws or the Sabbath? What was his resurrection like (cf. the four Gospels)? How are people saved (or get into heaven) and are sanctified by the Holy Spirit (Epistle to the Romans)? Why should Christians not subject themselves to an old-new law (Epistle to the Galatians)? And how should Christians live in the church and withstand persecution (Peter’s Epistle)?
Therefore, the New Testament authors, under the inspiration of the Holy Spirit, were not directed to develop the doctrine of the Trinity. Instead, they seemed to have assumed it, as we saw under point no. 1, and the four passages. They affirmed the full deity of Christ and the full deity and personhood of the Holy Spirit.
To repeat, Church fathers developed the doctrine of the Trinity from their reading of the New Testament, but they did not invent the doctrine out of thin air. For more information on the doctrine in the church fathers (post-apostolic church).