Definition and Background:
Circumcised believers, often referred to in the New Testament, are Jewish Christians who adhered to the practice of circumcision as a sign of the covenant between God and Abraham, as established in the Old Testament. This practice was a significant aspect of Jewish identity and religious observance, as outlined in Genesis 17:10-14, where God commands Abraham and his descendants to be circumcised as a perpetual covenant.

Old Testament Context:
Circumcision was instituted by God as a physical sign of His covenant with Abraham and his descendants. It was a requirement for all male members of the Israelite community, including servants and foreigners living among them. This rite was performed on the eighth day after birth, as specified in Leviticus 12:3. Circumcision symbolized the Israelites' unique relationship with God and their commitment to His laws.

New Testament Context:
In the New Testament, the term "circumcised believers" primarily refers to Jewish Christians who maintained the practice of circumcision even after accepting Jesus as the Messiah. The early church faced significant debates regarding the necessity of circumcision for Gentile converts. This issue is prominently addressed in the Acts of the Apostles and the Pauline Epistles.

Acts 15 and the Jerusalem Council:
The Jerusalem Council, as recorded in Acts 15, was convened to address the controversy over whether Gentile converts to Christianity were required to be circumcised and follow the Mosaic Law. Some believers from the Pharisaic tradition insisted on circumcision for salvation (Acts 15:1: "Some men came down from Judea and were teaching the brothers, 'Unless you are circumcised according to the custom of Moses, you cannot be saved.'"). However, the apostles and elders, guided by the Holy Spirit, concluded that circumcision was not necessary for Gentile believers, emphasizing salvation through grace and faith in Jesus Christ alone (Acts 15:11: "On the contrary, we believe it is through the grace of the Lord Jesus that we are saved, just as they are.").

Pauline Epistles:
The Apostle Paul addresses the issue of circumcision extensively in his letters, particularly in Galatians and Romans. Paul argues that physical circumcision is not a requirement for salvation and that true circumcision is a matter of the heart, by the Spirit, not by the written code (Romans 2:29: "No, a man is a Jew because he is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the written code. Such a man’s praise does not come from men, but from God."). In Galatians, Paul warns against relying on the law for justification, emphasizing that faith in Christ is the key to righteousness (Galatians 5:6: "For in Christ Jesus neither circumcision nor uncircumcision has any value. All that matters is faith, expressed through love.").

Cultural and Theological Significance:
The debate over circumcision in the early church highlights the transition from the Old Covenant, centered on the Law of Moses, to the New Covenant, centered on faith in Christ. Circumcised believers played a crucial role in this transition, as they navigated the complexities of maintaining their Jewish heritage while embracing the new faith in Jesus. The resolution of this issue underscored the universality of the Gospel and the inclusivity of the Christian community, transcending ethnic and cultural boundaries.

Conclusion:
The topic of circumcised believers in the New Testament serves as a testament to the early church's struggle to define the essence of Christian identity and the nature of salvation. It reflects the broader theological shift from a covenant based on physical signs and adherence to the law to one grounded in faith and the transformative work of the Holy Spirit.