Rom. 9:5 is really a confusion of subjects (rather than speakers) that we find in some trinitarian interpretations of this scripture.
Ro. 9:5 - " ... Christ came, who is over all, God blessed for ever. Amen." - KJV.
This is the scripture that A Catholic Dictionary calls
"the strongest statement of Christ's divinity in St. Paul, and, indeed, in the N[ew] T[estament]."
The Jerusalem Bible (Roman Catholic) renders it, like the equally trinitarian KJV, in such a way as to make Christ appear to be God: "Christ who is above all, God for ever blessed! Amen."
And the very trinitarian The NIV Study Bible, 1985, in a note for Ro. 9:5, calls it:
"One of the clearest statements of the deity of Jesus Christ found in the entire NT, assuming the accuracy of the translation (see NIV text note)."
Highly-regarded trinitarian NT scholar, F. F. Bruce writes concerning Ro. 9:5:
"God who is over all be blessed for ever. The relation of these words to those which precede is disputed. RSV takes them as an independent ascription of praise to God, prompted by the mention of God's crowning his many blessings on Israel by sending them the Messiah (similarly NEB, GNB)."
Bruce then gives reasons for and against such an understanding and concludes with:
"It is, on the other hand, impermissible to charge [accuse] those who prefer to treat the words as an independent doxology [praise to God] with Christological unorthodoxy. The words can indeed be so treated, and the decision about their construction involves a delicate assessment of the balance of probability this way and that." – p. 176, The Letter of Paul to the Romans, Tyndale New Testament Commentaries, Revised Ed., Eerdmans Publ., 1985.
However, The New International Dictionary of New Testament Theology is forced to acknowledge that even if such a trinitarian rendering of the Greek were accurate,
"Christ would not be equated absolutely with God, but only described as being of divine nature [see the DEF study.], for the word theos has no article. But this ascription of majesty does not occur anywhere else in Paul. The much more probable explanation is that the statement is a doxology [praise] directed to God." - Vol. 2, p. 80, 1986.
Trinitarian scholar John L. McKenzie also admits:
"Paul's normal usage is to restrict the noun [`God'] to designate the Father (cf 1 Co 8:6), and in Rm 9:5 it is very probable that the concluding words are a doxology, `Blessed is the God who is above all.'" – p. 318, Dictionary of the Bible, Macmillan Publ., 1979 printing.
The trinitarian United Bible Societies (UBS) makes the same admission:
"In fact, on the basis of the general tenor of his theology it was considered tantamount to impossible that Paul would have expressed Christ's greatness by calling him `God blessed for ever'." And, "Nowhere else in his genuine epistles does Paul ever designate ho christos [`the Christ'] as theos [`God' or `god']." - p. 522, A Textual Commentary on the Greek New Testament, United Bible Societies, 1971.
The UBS has therefore punctuated their NT Greek text in such a way as to show the separateness of Christ and God at Ro. 9:5.
Even A Catholic Dictionary admits the possibility that the scripture in question is really a doxology directed to God and not to Jesus:
"There is no reason in grammar or in the context which forbids us to translate `God, who is over all, be blessed for ever, Amen.' - a doxology suddenly introduced, but quite in St. Paul's manner (Gal. 1:5; cf. Rom. 1:25; 2 Cor. 11:31)." - p. 815.
And this statement is from the very same trinitarian reference work that calls Ro. 9:5 "the strongest statement of Christ's divinity" in the entire New Testament!! If this is the "strongest" such statement, where does that put the rest of the trinity "proof"?
Illustrating the high probability that the last part of Romans 9:5 is directed as a doxology to the Father, not to Jesus, are these translations of Ro. 9:5 found in trinitarian Bibles where the statement in question is not directed to Jesus:
The Revised Standard Version (RSV), 1971 ed. - "... of their race, according to the flesh, is the Christ. God who is over all be blessed for ever. Amen." - See p. 165, So Many Versions? (SMV), Zondervan, 1983.
The New American Bible (NAB), 1970 ed. - "... from them [Israelites] came the Messiah (I speak of his human origins). Blessed forever be God who is over all!"
The New American Bible (NAB), 1991 ed. - "[From the Israelites], according to the flesh, is the Messiah. God who is over all be blessed forever, Amen."
The New English Bible (NEB), 1961 ed. - "... from them, in natural descent, sprang the Messiah. May God, supreme above all, be blessed forever!"
Revised English Bible (REB), 1989 ed. - "... from them by natural descent came the Messiah. May God, supreme above all, be blessed forever!"
An American Translation (AT), 1975 printing - "... and from them physically Christ came - God who is over all be blessed for ever!"
Today's English Version (TEV), 1976 ed. - "Christ, as a human being, belongs to their race. May God, who rules over all, be praised forever!"
The Living Bible (LB) - "...Christ was one of you ... he who now rules over all things. Praise God forever!" - Tyndale House Publishers, 1971.
The Bible, A New Translation, (Mo) by Dr. James Moffatt, 1954 - "[From the Israelites] (so far as natural descent goes) is the Christ. (Blessed for evermore be the God who is over all! Amen.)" [Bracketed words are mine]
New Life Version (NLV) - "Christ himself was born of flesh from this family, and He is over all things. May God be honored and thanked forever." - Victor Books, 1993.
Not only can Ro. 9:5 be interpreted as having two different statements about two different subjects (1. Jesus came to earth as an Israelite, and, 2. Bless God who is over all.), but that is almost certainly the meaning intended by Paul (compare Ro. 15:5, 6; Ro. 16:27; 2 Cor. 1:3; Gal. 1:3-5; Eph. 1:3; 1 Tim. 1:16, 17).
Why, even the NIVSB, which called Ro. 9:5 "One of the clearest statements of the deity of Jesus Christ found in the entire NT" (see above), also gave the following in a footnote for Ro. 9:5 as proper alternate translations of this verse:
"Or Christ, who is over all. God be forever praised! Or Christ. God who is over all be forever praised!"
But some trinitarians have, instead, run these two separate statements of Jesus and God together in such a way as to give the impression that they both refer to the same subject: Jesus. The technique is identical with that of the "speaker confusion trick" we have been examining, and neither is acceptable as proper evidence for a "Jesus is God" faith!
[Comment by Ezra Abbot below added, thanks to ‘Yahoel.’ -
“The use of the word eulogetos, ‘blessed,’ which never occurs in the New Testament in reference to Christ. If we refer eulogetos to God, our passage [Ro. 9:5] accords with the doxologies Rom. i. 25; 2 Cor. i. 3; xi. 31; and Eph. i. 3. …. [This] strongly favors the reference of the eulogetos to God. It alone seems to me almost decisive.”
Abbot then discusses several other aspects of this verse and finally concludes that the understanding that the eulogy applies to God alone: "It is absolutely decisive." (p. 363) - Ezra Abbot, pp. 361-363, The Authorship of the Fourth Gospel. (emphasis added.)]