The phrase in question is ὁ Χριστὸς τὸ κατὰ σάρκα ὁ ὢν ἐπὶ πάντων θεὸς εὐλογητὸς εἰς τοὺς αἰῶνας. Here are the two possible translations, with some English translations that (more or less) follow this option.
1) Christ according to the flesh who is over all, God blessed forever (or "who is God over all, blessed forever"). KJV, NASB, NIV, NLT, ESV, NET, HCSB, NRSV.
2) Christ according to the flesh. God who is over all [be] blessed forever. RSV, CEV, NAB
Option 1 typically includes a comma, but the comma does not affect the meaning. Option 2 requires a period between κατὰ σάρκα and ὁ ὢν. It is legitimate for translators to insert periods where necessary, since ancient manuscripts used minimal punctuation. But it is important to note that no ancient manuscript inserted a period at that spot. The manuscript above is typical: there are punctuation marks after "promises" from Rom 9:4, and after "amen" in 9:5, but none after "according to the flesh" (line 4, fifth letter in the photo).
In favor of option 2: Although Paul elsewhere makes statements about the deity of Christ, he never does so in these words, equating Χριστὸς (Christ) with θεὸς (God). Elsewhere in the NT, the phrase "over all" and "blessed" (εὐλογητὸς) are used with reference to the Father, not the Son.
In favor of option 1: the phrase ὁ ὢν ("who is") is a participle phrase functioning as an adjective. Everywhere else in the New Testament and in the LXX, this phrase modifies a noun that precedes it. I cannot find any example of ὁ ὢν modifying a noun that follows. That means that ὁ ὢν must modify Christ, not God, resulting in "Christ... who is God." There are a few examples of other adjectival participles (i.e., not εἰμι) modifying a noun that follows, but they are quite rare.
I favor option 1 for three reasons.
- Translation decisions should rely heavily on original grammar, and the grammatical support for option 1 is much stronger than for option 2.
- The only real argument for option 2 is that Paul doesn't elsewhere use this kind of language to refer to Christ. But Paul often makes unique statements that have no exact parallel elsewhere in his writings. It is illegitimate to exclude a translation only because "it doesn't sound like Paul." If Paul wants to emphasize that Christ is God, it is only natural that he would use language that he has elsewhere used for God.
- Option 1 best makes sense of the context. Paul is expressing his anguish that so many of his fellow Israelites, who had the patriarchs, the Scriptures, and Christ himself, have rejected Christ. Paul emphasizes who they are rejecting: Christ who is Jewish in his humanity, but is also God over all, blessed forever.