As concerning the gospel, they are enemies for your sakes: but concerning the election, they are beloved for the fathers' sakes.
Read Chapter 11
Ambrosiaster
AD 400
However seriously the Jews may have sinned by rejecting the gift of God, and however worthy they may be of death, nevertheless, because they are the children of good people, whose privileges and many benefits from God they have received, they will be received with joy when they return to the faith, because God’s love for them is stirred up by the memory of their ancestors. Commentary on Paul’s Epistles.
According to the gospel, indeed, they are enemies for your sake. That is, enemies both to you, because they see the gospel preached and received by you, and enemies to God, because he has rejected them at present for their wilful blindness: yet according to election, God having once made them his elect, and because of their forefathers, the patriarchs, they are most dear for the sake of the fathers: for the gifts and the calling of God are without repentance, in as much as God is unchangeable, and his promises, made absolutely, cannot fail. (Witham)
When the Gentiles believed, the Jews became even more obnoxious. But even now God has not stopped calling the Gentiles. He is waiting for all of them who are to believe to come in, and then the rest of the Jews will come as well.