The Catholic Defender: For a Jewish person to convert to the Catholic Faith, they become a fullfilled Jew

Many Jewish converts to Catholicism view their faith journey as the fulfillment or completion of their Jewish heritage through the recognition of Jesus as the Messiah.

Fulfillment of Prophecy: Several high-profile converts and theologians—such as Roy Schoeman and the late Cardinal Jean-Marie Lustiger—describe embracing Christianity not as an abandonment of their heritage, but as reaching the intended destination of pre-Messianic Judaism.

Hebrew Catholics: Some converts identify as Hebrew Catholics or "Catholic Israelites," viewing themselves as members of the people of Israel who fully accept Catholic doctrine while retaining an ethnic and cultural connection to their roots

Ritual and Mosaic Law: Catholic teaching holds that the ceremonial and Mosaic laws (such as kosher dietary rules or physical circumcision) were preparatory and have been fulfilled by Christ and baptism; converts are not bound to follow them, though non-incompatible cultural traditions may be preserved

Jewish Reception: Mainstream Jewish communities generally view the adoption of Christian faith and baptism as a definitive break with the Jewish religion, making terms like "fulfilled Jew" controversial or rejected within normative Judaism.

Catholic Teaching: The Catholic Church explicitly rejects replacement theology, affirming per Nostra Aetate that God's covenant with the Jewish people remains irrevocable, while maintaining that the fullness of salvation is found in Jesus Christ.

The relationship between the Old and New Covenants is one of the most central and deeply debated frameworks in Christian theology, dictating how scripture is read, how salvation is understood, and how the church relates to ancient Israel. Theological writings generally approach this dynamic through three primary frameworks, varying on a spectrum from absolute continuity to distinct discontinuity.

Covenant theology, rooted deeply in Reformed tradition, views the relationship between the covenants as a single, overarching Covenant of Grace administered differently across history. 

The Core Premise: God established a "Covenant of Works" with Adam, which failed due to sin. Every subsequent covenant (Abrahamic, Mosaic, Davidic, and New) is an unfolding administration of the one Covenant of Grace. 

The Mosaic vs. New Dynamic: The Old (Mosaic) Covenant is not seen as an enemy to the New; rather, it was a "pedagogue" or a temporary administration meant to restrain sin and point to Christ. The moral law (the Decalogue) remains perfectly binding on New Covenant believers, while the ceremonial and civil laws are fulfilled and abrogated.