Do not cause anyone to stumble, whether Jews, Greeks or the church of God- I Corinthians 10:33, NIV
Paul was a universal preacher. He could, and did, talk to all kinds of people. But what are we to do with this division? Is it ethnic? If so, how is the church an ethnic group, as it is composed of both Jews and Greeks (Gentiles)?
And did not Paul offend? When he was stoned, was it not by those he offended?
I will be so bold as to say that Paul was writing about the elect. For he addressed each of these in his teaching. He spoke to Jews after he was converted, by appealing to their heritage and national promises, as in Romans chapter 11. He addressed the Greeks on Mars Hill. His letters to the churches of God are our most complete church epistles.
In these speeches and writings there is no offense to the elect, but so great an offense that he was under the sentence of death, finally committed in Rome. So to the elect, no offense, but to the non elect, great offense.
If you will allow me a brief "Columbo minute", since Paul listed both church and Israel as separate groups, how can the Church Replacement boys say that the church is Israel?