Ro 9:15 For He says to Moses, "I will have mercy on whomever I will have mercy, and I will have compassion on whomever I will have compassion."
God can do as He please. He is sovereign. If it pleased God to show mercy to non-Jews, He can do it. After all, God is the God of all men being their Creator, there is no other.
Ro 3:29 Or is He the God of the Jews only? Is He not also the God of the Gentiles? Yes, of the Gentiles also,
The purpose of Paul in writing this verse is not to limit and confine God's mercy on certain people called the elect. No, he cited this verse to show that God can have mercy on all, whether Jew or Gentile.
Ro 10:12 For there is no distinction between Jew and Greek, for the same Lord over all is rich to all who call upon Him.
Ro 11:32 For God has committed them all to disobedience, that He might have mercy on all.
Far from limiting God's mercy, Paul, in fact, used the verse to show that God is sovereign with His mercy. And He has sovereignly decided to have mercy and compassion, not just on Jews, but also on Gentiles who trust in His Son for salvation.
The Jews thought that salvation belonged only to Jews, since they were descendants of Abraham, they were given the covenants of God and the Law etc.
Paul says: "No, God can have mercy on anyone, not just Jews. His mercy is not confined to the physical descendants of Abraham. His mercy is not earned by law-keeping. No, it is given to those who have faith in Christ."
This has nothing to do with unconditional election to salvation of a few at all.
