Thank you for the theological question on Romans 9:5, “Do Trinitarians and Binitarians think Paul changed his teaching regarding Jesus (Rom 9:5)?”
If I may cite the broader context in answering one’s question, “I speak the truth in Christ—I am not lying, my conscience confirms it through the Holy Spirit— 2 I have great sorrow and unceasing anguish in my heart. 3 For I could wish that I myself were cursed and cut off from Christ for the sake of my people, those of my own race, 4 the people of Israel. Theirs is the adoption to sonship; theirs the divine glory, the covenants, the receiving of the law, the temple worship and the promises. 5 Theirs are the patriarchs, and from them is traced the human ancestry of the Messiah, who is God over all, forever praised! Amen.” (NIV).
Here are some observations for one’s consideration that the Apostle Paul did not change his teaching on Jesus as Trinitarians uphold the plurality of the Godhead by Paul.
A. The Apostle Paul mentions or infers the plurality of the Godhead.
As one reads the context, the Apostle Paul cites three persons in this passage: Christ, the Holy Spirit, and implies the God who gave the covenant to the Israelites.
It is the Creator God who gave the covenant to the Israelites (Exodus 19–20). Paul mentions the Holy Spirit as a witness of his anguish for the Jewish people. Lastly, Paul mentions Christ as speaking the truth in Christ, wish that he could be cursed and cut off from Christ for the sake of his people. Thus Paul declares his believe in the plurality of the Godhead.
The theological designation of the Trinity to describe the plurality of the God is a good one. That’s just my opinion.
B. The Apostle Paull cites the ancestry of Christ as from the Jewish lineage.
In verse 9, the Apostle Paul is presenting to the Jews in Rome that Jesus is from the line of David. He acknowledges the Jews have a special place in God’s program since God selected the Jews to be his people, gave them the covenant, and the temple worship. He even goes further into their history to the patriarchs to include Abraham, Isaac, and Jacob through the centuries to the time of Jesus Christ.
Although Paul doesn’t state the full lineage of Jesus, it is assumed that the Christian Jews or Jews would know that the promise of God is through Abraham. and through King David.
Matthew 2 says this, “After Jesus was born in Bethlehem in Judea, during the time of King Herod, Magi[a] from the east came to Jerusalem 2 and asked, “Where is the one who has been born king of the Jews? We saw his star when it rose and have come to worship him.” 3 When King Herod heard this he was disturbed, and all Jerusalem with him. 4 When he had called together all the people’s chief priests and teachers of the law, he asked them where the Messiah was to be born. 5 “In Bethlehem in Judea,” they replied, “for this is what the prophet has written: 6 “‘But you, Bethlehem, in the land of Judah, are by no means least among the rulers of Judah; for out of you will come a ruler who will shepherd my people Israel” (NIV).
C. The Apostle Paul also declares that the Christ is also God.
In verse 5, the Apostle Paul not only states the lineage of Jesus but his deity. Jesus is the God-Man. He states that the Christ is God over all. The emphasis is that the Christ is over all the Jews including the Gentiles. this Jesus is to rule over all people of the earth.
Christians who believe in the plurality of the Godhead of three persons in the Godhead affirms Paul’s declaration to the Romans. Paul didn’t change his view on the plurality of the Godhead as being three persons in one. He affirms the plurality of the Godhead with the Father, giver of the covenant, the Holy Spirit, and Jesus Christ.
There are other biblical passages that speaks on the plurality of the Godhead, but I am limiting to the passage being raised. I hope this helps explains how some Christians explain Romans 9:5.
SUMMARY: Christians who hold to the Trinitarian viewpoint affirm the Apostle Paul’s believe in the plurality of the Godhead includes the Father, the Holy Spirit, and Jesus Christ.
-Kingston