- It has Paul acclaiming Christ as God, which he does nowhere else;
- it is the only direct Pauline affirmation of Jesus as the Jewish messiah (albeit τὸ κατὰ σάρκα); and
- the sequence of ideas is garbled and abrupt (e.g., εὐλογητὸς almost always precedes θεὸς in a doxology).
Ἀλήθειαν λέγω ἐν Χριστῷ, οὐ ψεύδομαι, συμμαρτυρούσης μοι τῆς συνειδήσεώς μου ἐν πνεύματι ἁγίῳ, ὅτι λύπη μοί ἐστιν μεγάλη καὶ ἀδιάλειπτος ὀδύνη τῇ καρδίᾳ μου. ηὐχόμην γὰρ ἀνάθεμα εἶναι αὐτὸς ἐγὼ ἀπὸ τοῦ Χριστοῦ ὑπὲρ τῶν ἀδελφῶν μου τῶν συγγενῶν μου κατὰ σάρκα, οἵτινές εἰσιν Ἰσραηλῖται, ὧν ἡ υἱοθεσία καὶ ἡ δόξα καὶ αἱ διαθῆκαι καὶ ἡ νομοθεσία καὶ ἡ λατρεία καὶ αἱ ἐπαγγελίαι, ὧν οἱ πατέρες καὶ ἐξ ὧν ὁ Χριστὸς τὸ κατὰ σάρκα, ὁ ὢν ἐπὶ πάντων θεὸς εὐλογητὸς εἰς τοὺς αἰῶνας, ἀμήν.
There are at least two verbatim parallels:
Διὸ παρέδωκεν αὐτοὺς ὁ θεὸς ἐν ταῖς ἐπιθυμίαις τῶν καρδιῶν αὐτῶν εἰς ἀκαθαρσίαν τοῦ ἀτιμάζεσθαι τὰ σώματα αὐτῶν ἐν αὐτοῖς· 25οἵτινες μετήλλαξαν τὴν ἀλήθειαν τοῦ θεοῦ ἐν τῷ ψεύδει καὶ ἐσεβάσθησαν καὶ ἐλάτρευσαν τῇ κτίσει παρὰ τὸν κτίσαντα, ὅς ἐστιν εὐλογητὸς εἰς τοὺς αἰῶνας, ἀμήν.
2 Corinthians 11:31
ὁ θεὸς καὶ πατὴρ τοῦ κυρίου Ἰησοῦ οἶδεν, ὁ ὢν εὐλογητὸς εἰς τοὺς αἰῶνας, ὅτι οὐ ψεύδομαι.
In these latter two doxologies, the grammar is natural and the meaning is plain. The subject is God the creator/Father, and he is introduced first by a direct reference, and to him glory is given: who is [relative pronoun + verb] blessed unto the ages, and, the one being [article + participle] blessed unto the ages.
But in Romans 9, the apostle is somehow unable to make his meaning clear. If he had remembered himself from these previous passages, he could not have struggled to specify whether he is glorifying YHWH (the god of the Israelites, who are the topic of chapter 9); or rather ὁ Χριστὸς τὸ κατὰ σάρκα, as one must infer if the article + participle construction has any meaning.
In reality the meaning is not so unclear. But the doxology at the end does muddle things just enough to give hope to those uncomfortable with so high a Pauline christology.
Karl Barth has some interesting comments:
Raymond Brown also thinks that the canonical text has Paul calling Jesus God, because the grammar is simple and obvious. He equivocates with the same discomfort as Barth:The words ὁ ὢν ἐπὶ πάντων, etc. may be taken as a relative clause, of which ὁ Χριστὸς, the subject of the preceding sentence clause, is the antecedent. This is strongly supported by the analogous grammatical constructions at Rom 1:25 and 2 Cor 11:31. I cannot, however, bring myself to accept 'so unparalleled an attribution of θεὸς to the exalted Lord' (Zahn) for the following reasons: first, I do not find the attribution either in 2 Th 1:12 or in Tiutus 2:13; secondly, it does not seem to be required by Rom 10:11-14; thirdly, such an attribution would, in my judgment, betray a lack of delicacy of which a thinker and writer who differentiates so clearly as Paul does would hardly have been guilty; fourthly, the passage does not play as large a part in the early Christological controversies as it must have done, had it been taken in this way: quite apart from [the fact that] the phrase ἐπὶ πάντων θεὸς εὐλογητὸς occurs frequently in the Psalms where the reference to the God of Israel seems quite obvious.
The highlighted portions typify RB's habit of diplomatic, both-sides bullshit (typical for "centrists" in general) when he obviously knows exactly what the text says and cannot avoid accepting it. But he writes as though grammar were a "viewpoint" and merely a single piece of "evidence." Barth says much the same, but he cannot bring himself to accept the scripture for what it is, and thus hypothesizes a corruption of a now lost original verse lauding the God of Israel as their most important and sacred qualification. And what is more relevant to the question of Israel's status as the chosen people than the fact that their god is the One True God? Barth is right to complain that Romans 9 is strange not to assert this.From a grammatical viewpoint this [that Christ=God] is the better reading. Also, the contextual sequence is excellent; for, having spoken of Jesus' descent according to the flesh, Paul now emphasizes his position as God. The major objection to this interpretation is that nowhere else does Paul speak of Jesus as God. Distinguished scholars are aligned on both sides of the issue. Personally, I am swayed by the grammatical evidence in favor of [the interpretation] whereby the title "God" is given to Jesus. But one may claim no more than plausibility.
(An Introduction to New Testament Christology, pp. 182-3)
The root of the problem of Romans 9:5 is theological, not philological. It is not a question of "where to put the punctuation." Rather, the exegete or translator puts the punctuation wherever he does after he has made up his mind what the verse means. Thus the RSV gives
This translation is tendentious, because it simply ignores the repetition of the definite article ὁ in the phrase ὁ Χριστὸς τὸ κατὰ σάρκα ὁ ὢν ἐπὶ πάντων θεὸς, which secures the reference only to Christ.
There is no question that the grammar compels us to understand Paul attributing deity to Christ, in spite of the garbled quality of the whole verse that results from the combination of this affirmation about Christ's deity with the typical language of Pauline doxologies of God the Father/Creator, which in turn derives from the phrasing of the doxologies of YHWH in the LXX Psalms.
The text calls Christ God. Because this statement is genuinely un-Pauline, and most likely a mimicry of 2 Corinthians 11:31 and/or Romans 1:25 and/or the LXX Psalms, and ambiguously worded like many other fraudulent biblical texts, and an abrupt change of subject matter within the discourse about the people of Israel introduced at 9:1ff., I suggest that this is simply a late catholic interpolation. Traditional interpreters of Paul will reject this idea on principle, and cry out that there are no textual variants. But what could be more dear to the catholic editors of the NT than to exalt Christ's divinity, albeit with becoming scriptural ambiguity? And, of course, to silence anyone who doubted that Paul preached the same Jesus as the Evangelists.
It is not irrelevant that chapter 9 is entirely unattested by the witnesses to Marcion's text. Tertullian complains of an "immense chasm" (salio et hic amplissimum abruptum intercisae scripturae).
The lack of confidence that exegetes have demonstrated about Romans 9:5 for centuries probably betrays some suspicion that Paul would never have written it. But they don't want to name this suspicion, because it would then also cast doubt on the immediately previous assertion about the Jewish messiah. And they need that verse because nowhere else does Paul so much as seem to think of Jesus as a Jewish messiah, and the only reference to him as a recently historical man in Judea is the very doubtful 1 Th 2:14-16.