Pt 1 here
The Church is Central to the Christian in order to provide salvation to the Gentiles
Therefore remember that you, once Gentiles in the flesh–who are called Uncircumcision by what is called the Circumcision made in the flesh by hands– that at that time you were without Christ, being aliens from the commonwealth of Israel and strangers from the covenants of promise, having no hope and without God in the world. But now in Christ Jesus you who once were far off have been brought near by the blood of Christ.
For He Himself is our peace, who has made both one, and has broken down the middle wall of separation, having abolished in His flesh the enmity, that is, the law of commandments contained in ordinances, so as to create in Himself one new man from the two, thus making peace, and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity. And He came and preached peace to you who were afar off and to those who were near. For through Him we both have access by one Spirit to the Father.
Now, therefore, you are no longer strangers and foreigners, but fellow citizens with the saints and members of the household of God, having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone, in whom the whole building, being fitted together, grows into a holy temple in the Lord, in whom you also are being built together for a dwelling place of God in the Spirit.
(Eph 2:11-22 NKJV)
An argument of the centrality of the Church to the Christian is that it unites the Gentiles with the Jews into one body, that of Christ. Some modern theologians refute such ideas by drawing a line between Israel and the Church, making the Church seem second to that of Israel, however, in the writings of the Apostles, we find that the Church as superseded Israel and only in the Church is Israel made perfect, and not the other way around as John Hagee and others would have us believe.
Supersessionism, or Replacement Theology, is the idea that the Church is the completion, or perfection of the Israel, where Israel is united with Gentiles to form the Church, in one body. Paul says that we are built together, therefore to deny the place of Israel in the Church is to deny Paul. The Apostle also said that at one time we, Gentiles, were foriegners to the promises of Israel, and that by the blood of Christ, we are brought together and made one; to the place of the Church in Israel is to deny the body of Christ. To say that the Church replaced Israel is to deny a great many eternal truths., as God made a covenant with Israel which Paul refers to when he mentions the remnant in Romans; it is more appropriate to say that the Church superseded Israel as the people of God, as we are now one people under one name, and that name is not Israel.
Israel, the Jews, is no longer the chosen people of God. Instead, the Church (Jew, Gentile, Triumphant, Militant) is the Israel of God (Galatians 6.16). Many would proclaim that Israel has her own covenant with God, yet in John 14.6, Christ says that the only to the Father is through Him, making such ‘me too’ agreements null and void.
The prophecies pointing to a future Jerusalem point not to a city of stone, but a spiritual city, the Church.
But you, yes you!, have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to the numberless multitude of angels in joyful assembly, And to the church of the firstborn, who are recorded in heaven, and to God the Judge of all, and to the spirits of righteous men made perfect,
(Heb 12:22-23 CTV)
We are Jews, who are the Church, because the promises are no longer genetic, but based on the indwelling of the Spirit:
For he is not a Jew that is one on the outside, and neither is circumcision that which is physical But, he is a Jew that is one inwardly and circumcision is that of the heart — which is the work of the spirit and not of the letter of the Law — whose praise is not of man, but from God!
(Rom 2:28-29 CTV)
A good many of detractors to replacement theology call it ‘vile’ and ‘antisemitism’ while failing to understand that Scripture points squarely at the identity of the Church as both Jew and Gentile, neither Christ one above the other. Supersessionism provides for equality among Jews and Gentiles and is indeed the progenitor of the term ‘catholic’ itself pointing to the universal quality of the Church.
John Darby, and later, C.S. Scofield, popularized the notion, generally called Dispensationalism, that Israel was stood somehow separate from the Church in view of salvation and indeed of equality. This has given way to the pre-tribulation rapture dogma that has swept Protestant churches leading to the much read, much hated, series by Tim LeHaye and Jerry Jenkins, Left Behind. The idea is that after the Church has been ‘raptured’ the Jews will en masse turn to God and find their salvation out side of the Church (since the Church as left), while restoring the Temple and the Levitical Priesthood, along with sacrifices. Many of this persuasion see the Epistle to the Hebrews as a book written exclusively to the Jews after the Rapture, thus they deny the warnings against apostasy and the straightforward theology that declares that the Old Covenant was completed in the faithfulness of Christ.
The Centrality of the Church to the Christians brings perfection and salvation.
The Centrality of the Church to the Christian brings unity with the Jews and Israel, including the promises given to her patriarchs and all are made children of Abraham by faith. Without the Church, their is no unity, no union, no body of Christ and thus no promise of salvation for either the Jew or the Gentile, living or dead.