The Unity of God's Covenant People
To understand the relationship between the Church and Ethnic Israel, I encourage you to first and foremost submit your thinking to the whole counsel of scripture and find your method of interpreting of the Bible from the Bible itself! Wisdom does not come on this issue from extra-biblical sources but rather we must ask the Holy Spirit to help us understand the Word, and, according to the Word, the meaning of the Law and Prophets are found and explained in Jesus Christ.
The Apostle said, "no matter how many promises God has made, they are "yes" in Christ" (2 Cor. 1:20), These very promises are the fulfillment of the covenant blessings promised to Abraham that all the people's of the earth would be blessed through Him. "He redeemed us in order that the blessing promised to Abraham might come to the Gentiles through Christ Jesus, so that by faith we might receive the promise of the Spirit" (Galatians 3:14). The kingdom of God is a kingdom only because Jesus is the King who reigns over it and so only those who are united to Christ are members of this kingdom.
Throughout Church history there have been three main systems of theology that have tried to explain the relationship between the physical decendants of Abraham (ethnic Jews) and the apostolic church which is comprised of Jews and Gentiles:
1) Made popular by the the teachings of Darby and the Scofield Reference Bible, Dispensationalism has held the majority report in the last century among American Evangelicals. According to this viewpoint Israel (ethnic Jews) are radically distinct from the church. They will rule the earth from the land of Israel for 1000 years after Jesus returns and raptures Christians. The church, in this system is to await the new earth after the 1000 years is complete. Some more radical forms of Dispensationalism called Christian Zionists believe that one of the churches' main objectives today is to support ethnic Israel. This is based on the promise of blessings and curses God gives to Abraham and his seed.
2) Another system which tries to explain the relationship beteen ethnic Isreal and the church is called replacement theology or suppercessionism. This has been the majority theology through church history in the Roman Catholic church and has even influenced some Protestants. This system affirms that God has basically cut off all his covenant relationships with ethic Jews and has replaced his covenant people with the Church. This type of theology has had the most influence up to sometime in the middle of the 20th century with the majority of Christians worldwide.
3) But the last system, which I believe is the most biblical one, is one in which God's people throughout the ages are unified in Christ, even though those with less revelation may have understood Christ in a dimmer light. This difference here is not unlike the difference of a new tree with a sprout coming out of the ground and a tree which is full grown. Both are the same tree, just at different degree of organic maturity. One is in a dark room with a candle and the other with the lights turned on. Both are in the same room however.This is often called realized eschatology or covenant theology (held by most recent scholars of biblical theology, Historic Premillenialists, Amillennialists, Postmillenialists & So-called progressive Dispensationalists) The Jews anticipated Christ's coming and the church reflects back on it. Both are equally part of the body of Christ - for salvation for believers in the Old Testament and New is found in Christ alone. According to Paul, the definition of a true Jew is one who obeys the law of God from the heart. This being the case, there was only one True Jew who ever lived: Jesus Christ. He is the remnant of one, the true Israel of God whom both Jews and Gentiles are grafted into and in whom share spiritual blessings. Therefore there is a unity of God's covenant working between the time of Ethic Israel and after Pentecost. So the old covenant has never been replaced by the new. but rather, expanded upon. First God revealed Himself to mostly Jews but now He includes both Jew and Gentile. This perspective views Salvation as being just as gracious in the Old Covenant as the New, both which receive through faith in Christ. As Paul wrote, the gospel was preached to Abraham beforehand. Although the church no longer has national boundaries. like ethnic Israel, the Holy Spirit unites both of us to Christ who writes the Law of God in our hearts (Romans 4:16-18; 11:17-21; Galatians 3:14; ) We are "no longer foreigners and aliens, but fellow citizens with God's people".
Romans 9 teaches that not all Israel is Israel ... showing that not all of Abraham's physicall decedants were part of God's plan of blessing. Only the people of promise, those circumcised in heart. Now is no different but includes both ethnic Israel and all the Gentiles who are united to Christ by grace through faith. Again, "no matter how many promises God has made, they are "yes" in Christ" (2 Cor. 1:20),