Paul refers to the civil and ceremonial laws of the old covenant, specifically the purity laws that distinguished Israel from the nations around her.1 This law set up a wall of partition (Ephesians 2:14) that has been destroyed by the work of Christ and now also through the preaching of the gospel.2 When Paul preached justification by faith, he removed the barriers between Jew and Gentile.
18 For if I rebuild what I tore down, I prove myself to be a transgressor.