Ephesians 2.19. Then accordingly, you are no longer strangers and aliens, but fellow-citizens with the holy-ones, and of the household of God. 20. And are built over the foundation of the Apostles and Prophets, and the Cornerstone Himself-- Jesus Christ. 21. In whom all the building fit together is caused to grow into a temple, holy unto the Lord. 22. In whom you also are built as a dwelling for God in the Spirit.
Paul shows the Gentile believers in the area of Ephesus their standing before God. There must have been some questions concerning their position as to their citizenship within the body of Christ as well as in the history of the Church (both Old and New Economies). The Apostle answers these questions with great pastoral clarity and compassion. The Gentile believers are not second-class citizens within the household of faith, but are being built upon the same foundation as the Jewish believers past and present.
The foundation on which these believers are being built is the one that has been laid by the Testaments of the Old Economy as well as the New Economy. The Old Economy was laid by the Prophets of old. They were the ones who brought the Word of God, the oracles of God, the thoughts and rebukes of God. The Prophets were the primary writers of the Old Economy and held the schools of prophecy to ensure the preaching of the Word for the covenant people.
The New Testament section of the foundation was laid by the Apostles. The Apostles were the ones who learned at the feet of Christ; they were given the ordination by Christ to preach the Word and to dispense of the sacraments. The Apostles of the New, as the Prophets of Old, were entrusted to ensure the carrying on of preaching, the administration of the sacraments, and the proper use of discipline. The Apostles are the primary Words that are read and studied in the Church today as the Prophets were in the Old Covenant.
The Cornerstone is Jesus Christ. A cornerstone, as a tool of architecture, is important to be laid as straight as possible, since it is the stone by which all other stones will be laid. If the cornerstone is not straight then the rest of a building will be crooked. Jesus Christ is the canon by which all believers are to judge themselves as well as the standard by which all Churches measure their faithfulness.
The purpose of this allegorical building is so that a spiritual habitation can be made for the Spirit of God as well as to grow spiritually in holiness. This needs to be reflected in the Church as the Gentiles as well as the Jews who believe attempt to live lives that are holy and set apart for the use of the Lord. The Church is also to be a dwelling place that is fit for the Spirit of God. A dwelling place for God must be holy and cleansed, and this is what Paul is promoting, as well as the Church of Ephesus is to be set apart for a fit dwelling of the Spirit of God.