OIC, thanks! This is from Hebrews 8:8-12. Here St. Paul is quoting Jeremiah 31:31-34 where Jeremiah prophesies that God will give a new law to his people inscribed on their hearts and not on stone tablets. In Jeremiah's mind, this probably referred to historical OT Israel where the divided houses of Israel (10 northern tribes of Israel and 2 southern tribes of Judah and Benjamin) would again be united into one.
In NT thought, however, (including here in Hebrews) Israel refers to the New Israel, the Church, called "the Israel of God" (Galatians 6:16), which is heir to the covenant promises made by God. St. Paul sees the "Israel of God" in contrast to "Israel according to the flesh" (1 Corinthians 10:18).
From the Catechism:
762 The remote preparation for this gathering together of the People of God begins when he calls Abraham and promises that he will become the father of a great people. Its immediate preparation begins with Israel's election as the People of God. By this election, Israel is to be the sign of the future gathering of all nations. But the prophets accuse Israel of breaking the covenant and behaving like a prostitute. They announce a new and eternal covenant. "Christ instituted this New Covenant."
765 The Lord Jesus endowed his community with a structure that will remain until the Kingdom is fully achieved. Before all else there is the choice of the Twelve with Peter as their head. Representing the twelve tribes of Israel, they are the foundation stones of the new Jerusalem. The Twelve and the other disciples share in Christ's mission and his power, but also in his lot. By all his actions, Christ prepares and builds his Church.
Thank you!!!