Is God the God of Jews only?...

No, He is the God of Gentiles also.

Notice the importance of the Jew, in Paul’s thinking, with the Gentile being of secondary emphasis.

Is important to keep in mind that the Jew always is first in the plan of God. Because God has dispersed the Jews for two thousand years, the Gentiles have assumed that they have inherited the place in God’s Kingdom formerly held by Jews.

This is not the case. Christianity in the beginning was a Jewish religion and will once again be a Jewish religion when the Lord gathers His people from the ends of the earth. We Gentiles are guests at the banquet.