Galatians

see here: http://www.calledtocommunion.com/2009/12/justification-catholic-church-and-the-judaizers/

 Returning to the Old Covenant, when the New Covenant has been revealed, is to reject Christ, His atonement, and the grace that comes through His atonement. That’s just what St. Paul is saying in his letter to the Galatians.