Hopefully to build on the discussion in the SB...
There is much out there on this but a quick google found this already:
The New Catholic Encyclopedia states: “The formulation ‘one God in three Persons’ was not solidly established, certainly not fully assimilated into Christian life and its profession of faith, prior to the end of the 4th century. But it is precisely this formulation that has first claim to the title the Trinitarian dogma. Among the Apostolic Fathers, there had been nothing even remotely approaching such a mentality or perspective.”—(1967), Vol. XIV, p. 299.
Reminds me of other doctrines developed over time and with councils...
For those with more interest and more time:
Small wonder the East vs West remain still at odds on this construction...from tradition.
As for Paul:
1 Corinthians 8:5-6 “For even if there are so-called gods, whether in heaven or on earth (as indeed there are many “gods” and many “lords”), yet for us there is but one God, the Father, from whom all things came and for whom we live; and there is but one Lord, Jesus Christ, through whom all things came and through whom we live.” - New International Version
1 Corinthians 15:24-28 “Then the end will come, when he hands over the kingdom to God the Father after he has destroyed all dominion, authority, and power. For he must reign until he has put all his enemies under his feet. The last enemy to be destroyed is death. For “God has put everything under his feet” Now when it says that everything has been put under him, this clearly does not include the One who put everything under him. And when all things have been subjected to him, then the Son himself will be made subject to Him who put all things under him, so that God may be all in all.”
1 Corinthians 11:2,3 “But I want you to understand that the head of every man is Christ, and the head of the woman is man, and the head of Christ is God”.
2 Corinthians 1:1-3 “Paul, an apostle of Christ Jesus by the will of God, and Timothy our brother, To the church of God in Corinth, together with all the saints throughout Achaia: Grace and peace to you from God our Father and the Lord Jesus Christ. Blessed be the God and Father of our Lord Jesus Christ, the Father of compassion and the God of all comfort,…”
Colossians 1:15 He is the image of the invisible God, the first-born of all creation.
Romans 15:5,6 “May the God who gives endurance and encouragement give you the same attitude of mind toward each other that Christ Jesus had, so that with one mind and one voice you may glorify the God and Father of our Lord Jesus Christ.”
By the time of Paul's arrest and trial in 57-59AD he had written Galatians both Thessalonians both Corinthians and Romans.
All of which could have been presented as material evidence against him...any of his NEW teaching...his ANOTHER gospel...which would be significant crimes against both the Temple and da joos traditions...
But Luke had Paul saying:
Acts 24:13 "Neither can they prove the things whereof they now accuse me."
Acts 23:9
A great clamor arose, and some scribes from the party of the Pharisees got up and contended sharply, “We find nothing wrong with this man. What if a spirit or an angel has spoken to him?” 10The dispute grew so violent that the commander was afraid they would tear Paul to pieces. He ordered the soldiers to go down and remove him by force and bring him into the barracks."
Acts 24:20 "...let these men state for themselves any crime they found in me when I stood before the Sanhedrin, 21
unless it was this one thing I called out as I stood in their presence: ‘It is concerning the resurrection of the dead that I am on trial before you today.’”
Acts 26:6 "And now I stand on trial because of my hope in the promise that God made to our fathers, 7
the promise our twelve tribes are hoping to realize as they earnestly serve God day and night. It is because of this hope, O king, that I am accused by the Jews. 8Why would any of you consider it incredible that God raises the dead?"
Years earlier Gamaliel had advised joos wanting to KILL Peter and the disciples for teaching and preaching One resurrected and in His name:
Acts 5:38 Therefore, in the present case I advise you:
Leave these men alone! Let them go! For if their purpose or activity is of human origin, it will fail. 39 But if it is from God, you will not be able to stop these men; you will only find yourselves fighting against God.”
I don't think the Pharisees before the Sanhedrin at Paul's trial would have vouched for him "We find nothing wrong with this man." or Gamaliel would have defended the disciples had any of them been preaching and teaching anything other than "Hear oh Israel our God is One"