John Chrysostom
"Or is God the God of Jews only?" Here he is saying something like this: Why does it seem absurd to you that every man is saved? Is God a private God?
By this he shows that those who wish to abase the Gentiles offend the glory of God even more, if they do not allow that He is the God of all.
If He is the God of all, then He cares for all. If He cares for all, then He saves all equally through faith. Therefore the Apostle says, "Or is God the God of Jews only, and not also of Gentiles? Yes, of Gentiles also."
God is not a private God, as is imagined in Greek myths, but common to all and one. Therefore he adds, "since God is one."