When: Early Church period

Where: Judea, Rome, Galatia

Central Error: Observance of the Mosaic Law was required for salvation

Description: This heresy is unique in that it's one of the few that's explicitly mentioned in the Bible. In Acts 15:1 we read;

And some coming down from Judea, taught the brethren: That except you be circumcised after the manner of Moses, you cannot be saved.

The Judaizers, as they've come to be known, were Jewish Christians who preached that the observance of the Mosaic Law was required in order to be saved; observance of Jewish dietary laws, Jewish feast days, and especially circumcision, were all required in order to come to Jesus. Basically, they preached that one had to become a Jew in order to become a Christian.

Saint Paul fought against this error, especially in his Epistle to the Galatians (Galatians 5:6), and the heresy was eventually decisively condemned at the Council of Jerusalem described in Acts 15.

Modern Manifestations: Many Christian and quasi-Christian movements today express elements of Judaizer error
- Messianic Judaism, which seeks to blend Jewish and Christian theology and preaches observing Jewish law.

- The Sabbatarian movement, which insists that the observance of the Jewish Sabbath (Saturday worship) is obligatory for Christians. The most well known Sabbatarian sect is the Seventh-Day Adventist (SDA) church.

- Quasi-Christian Judaizer groups include; the Worldwide Church of God (Armstrongism), the World Mission Society Church of God (observance of Saturday worship and Jewish feast days), the House of Yahweh in Texas (which also rejects the Trinity), etc.