Thomas Aquinas

“ But nothing save mortal sin hinders us from receiving Christ's fruit. Therefore since Christ's Passion it is a mortal sin to be circumcised, or to observe the other legal ceremonies.
I answer that, All ceremonies are professions of faith, in which the interior worship of God consists. Now man can make profession of his inward faith, by deeds as well as by words: and in either profession, if he make a false declaration, he sins mortally. ”

“ This pretense, however, is to be understood, not as though they did not in reality perform those actions, but in the sense that they performed them without the mind to observe the ceremonies of the Law: thus a man might cut away his foreskin for health's sake, not with the intention of observing legal circumcision.
But since it seems unbecoming that the apostles, in order to avoid scandal, should have hidden things pertaining to the truth of life and doctrine, and that they should have made use of pretense, in things pertaining to the salvation of the faithful ”

“ In like manner the ceremonies of the Old Law betokened Christ as having yet to be born and to suffer: whereas our sacraments signify Him as already born and having suffered. Consequently, just as it would be a mortal sin now for anyone, in making a profession of faith, to say that Christ is yet to be born, which the fathers of old said devoutly and truthfully; so too it would be a mortal sin now to observe those ceremonies which the fathers of old fulfilled with devotion and fidelity. ”