The Messianic cult

[Soyeong]

Paul answer this in Romans 3:28 A person is not a Jew who is one only outwardly, nor is circumcision merely outward and physical. 29 No, a person is a Jew who is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a person’s praise is not from other people, but from God.

In short a Jew is only a Jew if they have accepted Jesus.

In Romans 2:25-29, the way to recognize that a Gentile has a circumcised heart is by observing their obedience to God's law, which is the same way to tell for a Jew (Deuteronomy 30:6), and circumcision of the heart is a matter of the Spirit, which is in contrast with Acts 7:51-53, where those who have uncircumcised hearts resist the Spirit and do not obey God's law.