Paul, the “apostle to the pagans,” never abandoned his Jewish roots. If the pagan world was to be summoned to worship the one true God and to be grafted upon God’s people, it was because the God of Israel had fulfilled his ancient promises.
In his letter to the Romans, Paul argues that God’s promises to Israel had come true in Jesus, the Messiah. His key expression for this is “the righteousness of God.”
“Righteous” and its cognates are tricky. They translate the same Greek word group as “just” and “justify”; these terms evoke biblical passages, not least of all Isaiah 40–55, concerning the faithfulness of Israel’s God to the covenant. This “covenant faithfulness” is the reason why God will rescue Israel and so bless the whole world. “God’s righteousness,” with this meaning, resonates through postbiblical Jewish literature, as in the Dead Sea Scrolls. God’s rescue of Israel will be the great revelation in action of his “righteousness,” his tsedakah, his covenant faithfulness.