But I certify you, brethren, that the gospel which was preached of me is not after man.
For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ.
Galatians 1:11–12
The doctrine of the Trinity is something received from men and taught by men;
it did not come through the revelation of Jesus Christ.
There is a definite point in history when the Trinity was adopted as a theological doctrine within Christianity.
However, the truth that there is no God besides Jehovah is an eternal truth
that has existed from everlasting to everlasting.
Paul came to realize that the risen God whom he encountered on the road to Damascus was Yehowah God,
the One spoken of in the Old Testament Scriptures, who had promised to come as a child and abolish death.
He understood that Jehovah God, revealed in the writings of Moses, is Jesus. Therefore,
when he wrote to the church in Rome, he clearly proclaimed what that gospel is:
The gospel he promised beforehand through his prophets
in the Holy Scriptures regarding his Son,
who as to his earthly life was a descendant of David,
and who through the Spirit of holiness was declared to be the Son of God
with power by his resurrection from the dead—Jesus Christ our Lord.
Romans 1:2–4
But though we, or an angel from heaven, preach any other gospel unto you
than that which we have preached unto you, let him be accursed.
As we said before, so say I now again,
If any man preach any other gospel unto you than that ye have received,
let him be accursed. Galatians 1:8–9