In the Old Testament there are hints of gentiles coming to faith but for the most part the Church was a mystery until Jesus said in Mat 16:18 "And I tell you, you are Peter, and on this rock I will build my church, and the gates of hell shall not prevail against it." The Church was melting pot of the Lord for whosoever would believe both Jew and Gentile. However, the Church does not replace the nation of Israel in the plan of God for this world. They have a role to play in the future when they, as a nation, will receive Jesus as their Messiah.