Reformed interpretation of Scripture has traditionally insisted on the continuity of a single covenant of grace, proving the truth of the new covenant church being a continuation of the original covenant people of God.
This accords with the language of kahal (“assembly,” “congregation”), which the Greek version of the Old Testament translates: synagoge or ekklesia, which is then carried over into the New Testament designation for the people of God. Israel is the recipient of the laws and promises, the covenants of Sinai and Abraham, and whatever happens to extend the family is in fact an expansion rather than replacement of Israel. It is through the earthly, physical, ethnic Israel of God that the covenant of grace has unfolded throughout history and now reaches outward to all the nations and peoples of the world.
The attitude of the New Testament is quite clear. Jews labor under the illusion that they have some sort of advantage in being descended from Abraham.
In so thinking, they are thoroughly mistaken. Being descended from Abraham is no advantage whatsoever. God is able to declare anyone a child of Abraham; God is able from these stones to raise up children of Abraham. Matthew 3:8-9 And Paul confirms this by pointing out that not all of Abraham’s children were of Israel. Isaac was of Israel but Esau was not. So being a physical descendant of Abraham does not make one a child of the promise. By quoting the verses from Hosea, Paul says that God can take individuals who are not chosen and make them chosen. Romans 9:24-26 God is not bound by genealogical considerations… This is presumably the church which is not a natural family characterized by descent from a common ancestor but an association of persons from many peoples united by a common faith. Revelation 5:9-10 Therefore it is every faithful Christ follower and keeper of His Commandments, who are the real Israel of God.
As Israel’s exile testified, God had not reneged on his promise; Israel had reneged on hers. This point is as clear in the prophets as it is in Paul. God would still fulfill the purposes of his eternal election, however, and the Abrahamic promise envisioned this as the blessing that would come to all peoples through the Seed of Abraham and Sarah. That is: through Jesus. As with Eden, there is no way back to Sinai, but this is actually good news, since no one could be saved according to the righteousness of the law. The only way to be saved, and therefore, to belong to the true Israel of God, is to be “in Christ.” At Mount Sinai, Israel responded to the conditional terms as one person: “All this we will do!”, yet broke their covenant oath. At Mount Calvary, the True Israel, who had fulfilled the terms throughout his life, cried out, “It is finished!”
At the Synod of Jerusalem, this Christ centred interpretation of election and redefinition of Israel in line with the prophetic texts was officially adopted and it was Peter who gave such eloquent testimony to this interpretation that Gentile believers, no less than Jews, are justified by grace through faith without any distinction. Acts 15:8-11 Circumcision counts for nothing: everything turns on faith in Christ, announced by the gospel. Romans 2:17-29
The attitude we must have toward ethnic Jews is that of Paul the Jewish apostle to the Gentiles, who would have willingly born Israel’s “anathema” in her place. Romans 10:1-3
At the same time, we must remember that this anathema is not over Jews as Jews, but over all of humanity who are living apart from Christ. If we really follow through with the Pauline logic (maintained elsewhere in the New Testament, as it was throughout the prophets), there is no more guarantee that a particular visible church that bears the name Christian will not fail to have its candlestick removed should it live by any principle other than faith in Christ.
It is therefore, not ultimately a question of whether one is a Jew or a Christian in terms of outward organization, but of whether one is “inwardly circumcised”, that is: born again into Christ. Jesus is not only the high Priest and mediator of the Covenant; He is in his very person “a covenant to the people”. Isaiah 42:6
The problem is that the Old Covenant that the people made with God at Sinai was being allowed to determine the answer to these questions:
How are we saved? By fulfilling the law. Who is Israel? Those who fulfill the law.
Paul held this view before his conversion, as a Pharisee and persecutor of the church, but on the Damascus Road everything was turned upside down when he encountered a vision of the very “cursed” one according to the law. cursed is everyone who hangs on a tree, triumphantly seated at the Father’s right hand in glory. Now the questions receive different answers that are, in fact, perfectly consistent with the expectations of the prophets.
How are we saved? We are saved in the same way that all of the saints in redemptive history were saved: by belief in God and trusting in God’s promised Messiah.
Who are the people of God? The children of promise: those who share Abraham’s faith. The heirs of the Sinai Covenant are those who are ethnic descendants of Abraham, circumcised in the flesh; the heirs of the Abrahamic covenant (fulfilled in the New Covenant) are: all people, Jew and Gentile, who are “in Christ” through faith alone, circumcised in their hearts.
God’s faithful Christian people, His Victorious ones, [as seen in each of the seven Churchs of Revelation] and His Overcomers. Literally the Israelites of God. Galatians 6:16
The Prophetic Word 