I had someone ask me if Gentile Christians are Jews. This person has a friend who gave Romans 2:28-29 and Romans 9:6 as proof that Christians are Jews and the church is spiritual Israel. They were also told that the church should observe Jewish holy days like the Passover and worship on the Jewish Sabbath which is Saturday. They were also told that the covenants and promises given to Israel are transferred to the Gentile church. And last of all, my friend was told that their church (a Southern Baptist Church) was teaching false doctrines. Below is my answer.
That comes from replacement theology and shallow teachers. The passage in Romans 2 must be taken in context. Verses 28-29 fall into the larger section of Romans 2:17—3:20 in which Paul’s subject is ethnic Israel. In Romans 2:28–29 Paul spoke exclusively of Jewish people. He was making the point that a true “Jew” is one who trusts in God through faith in Christ. These verses cannot teach that Gentiles are spiritual Jews because Gentiles were not even being discussed. Paul was simply distinguishing between Jewish people who believe in Jesus and Jewish people who do not. In Romans 9:6 Paul was once again speaking exclusively of the Jewish people, teaching there is spiritual Israel inside of physical Israel; and he identified the believing Jewish remnant as true Israel.
The person who asked me thought maybe their friend was in a cult. There are cults who teach this doctrine but there are a few Christian churches who teach replacement theology. Most of them think they have stumbled upon a deep truth that everyone else has missed. Most of them lack humility and like I said, they think they are deep into the Word! In reality, they are very shallow not studying the Word of God Contextually, grammatically and historically. They worship on the Jewish Sabbath, observe Passover and do a few other things that were given only to Israel. Most of them take pride in telling true Christians that we are in false churches.
My professor in Bible College who taught Evangelism was a Jew and he considered all replacement theology cultic. So be careful who and what you listen to. There are a lot of cults out there who look like the real thing. There are also some shallow Christians who will take you down a legalistic road by spiritualizing the scriptures. And be careful of those who think they have this deep understanding of the Word of God! God Bless!