The Gentiles/Greeks responded to the good news of being reconciled to God through Christ’s life, death and resurrection. In contrast, fewer in the Jewish community had come to that same faith in Christ.
Paul was pointing out that God had been patient and was showing mercy to all so that they might come to faith in Christ. God could have judged and shown no mercy. But God wanted reconciliation with all people and was willing to work/wait patiently for it to occur.
In the Old Testament scriptures, a remnant in Israel was to endure and return to both God and the land. The Old Testament scriptures also hinted at others joining with Israel as being God’s people. For Paul these others were the Gentiles/Greeks that responded in faith to the good news of Christ as Lord and savior.
The promises of God belonged to those of faith whether they were Jew or Gentile/Greek.