Why do Catholics not follow all the Old Testament laws?

Catholics do not follow every Old Testament law because Jesus fulfilled the Old Covenant and established the New Covenant. Its ritual and national regulations no longer bind Christians, while its moral truth remains and is perfected in Christ.

Different kinds of commands served different purposes. The Law of Moses included moral prescriptions, liturgical rules, and laws governing Israel as a particular nation (CCC 1961-1962). The moral law is summarized in the Ten Commandments. Other commands regulated sacrifices, ritual purity, circumcision, food, clothing, festivals, and Israel's civil life. These prepared God's people for Christ and marked Israel off for its special covenant mission.

Jesus fulfilled the Law. Christ said, "I have come not to abolish but to fulfill" (Mt 5:17). Fulfillment means that the Law reaches its intended goal in Him. The temple sacrifices pointed toward His one perfect sacrifice. The Passover anticipated His saving death. Ritual washings prepared for the cleansing He gives. Christ also taught that foods do not morally defile the human heart (Mk 7:18-23).

The apostles settled the question. Some early Christians argued that Gentile converts had to be circumcised and keep the full Mosaic Law. At the Council of Jerusalem, the apostles, under the guidance of the Holy Spirit, rejected that requirement (Acts 15:1-29). St. Paul taught that circumcision and the ceremonial observances could not be imposed as conditions of salvation in Christ (Gal 5:2-6). Christians therefore do not offer animal sacrifices, observe kosher restrictions, or enforce the civil penalties of ancient Israel.

The moral law still binds. Murder, adultery, theft, idolatry, and false witness remain sinful. The Ten Commandments retain their authority for Christians (CCC 2068). Jesus deepens them by addressing the heart: anger can violate the command against murder, and lust violates marital purity (Mt 5:21-30). The New Law is chiefly the grace of the Holy Spirit, expressed in faith working through love and in Christ's teaching (CCC 1965-1972).

Catholics should avoid selecting Old Testament commands without considering their covenant setting and fulfillment in Christ. When a difficult law appears, read it alongside the Gospels, Acts 15, and the Church's teaching on the Old and New Laws.