"If you live not in the body which is Christ, you are none of His. Whose, then, are you? You have been cut off and will wither, and like the branch pruned from the vine, you will burn in the fire - an end which may God's goodness keep far from you. So little does the Roman Church stand alone, as you think, that in the whole world any nation that in its pride dissents from her is in no way a church, but a council of heretics, a conventicle of schismatics, and a synagogue of Satan." [ Pope Saint Leo IX ]
"To use the words of the fathers of Trent, it is certain that the Church 'was instructed by Jesus Christ and His Apostles and that all truth was daily taught it by the inspiration of the Holy Spirit.' Therefore, it is obviously absurd and injurious to propose a certain 'restoration and regeneration' for her as though necessary for her safety and growth, as if she could be considered subject to defect or obscuration or other misfortune. Indeed these authors of novelties consider that a 'foundation may be laid of a new human institution,' and what Cyprian detested may come to pass, that what was a divine thing 'may become a human church.'" [Pope Gregory XVI, Mirari Vos, August 15, 1832.]
"Blind they are ...they pervert the eternal concepts of truth ...they are seen to be under the sway of a blind and unchecked passion for novelty ...despising holy and Apostolic Traditions they embrace other and vain, futile, uncertain doctrines, condemned by the Church." [ Pope Gregory XVI, Singular Nos, June 25, 1834. ]