Is he the God of the Jews only? is he not also of the Gentiles? Yes, of the Gentiles also:
Read Chapter 3
Ambrosiaster
AD 400
Undoubtedly there is only one God for everybody. For even the Jews cannot claim that their God is not the God of the Gentiles also, because they believe that the origin of all people is from the one Adam and that no one who comes willingly to the law may be prevented from accepting it. Some Gentiles actually went with the Israelites into the desert of Egypt, and the Israelites were ordered to accept them as long as they agreed to be circumcised and eat unleavened bread, or the Passover, together with the rest of them. Then again Cornelius, a Gentile who was not judaized, received the gift of God, and it is clear from holy Scripture that he was justified. Commentary on Paul’s Epistles.
"Is He the God of the Jews only, and not also of the Gentiles? Yes, also of the Gentiles: if indeed He is one God".
For if to live well and according to the law is to live, also to live rationally according to the law is to live; and those who lived rightly before the Law were classed under faith,
One righteous person is no different from another righteous person, whether Jew or Greek. For God is not only the Lord of the Jews but of all humanity. He is the Father of all who know him. To live well and according to the law is to live. To live rationally according to reason is to live. Those who lived rightly before the law were classed under faith and judged to be righteous. Those who were outside the law, having lived rightly, on hearing the voice of the Lord … may turn and believe with all speed.
The apostle here tells us that all men are the creatures of God Almighty, and destined to eternal happiness. Neither was it necessary to be incorporated with the Jews by circumcision, to be made partakers of the justice of God. (Estius)
Paul shows that the Jews, by trying to put the Gentiles in their place, were insulting God’s glory by not allowing him to be the God of all. But if God is God of all, then he takes care of all, and if he takes care of all, then he saves all alike by faith.