From art. 4 of Traditi Humilitati, against indifferentism, a baneful heresy that is creeping around again:
4. Among these heresies belongs that foul contrivance of the sophists of this age who do not admit any difference among the different professions of faith and who think that the portal of eternal salvation opens for all from any religion. They, therefore, label with the stigma of levity and stupidity those who, having abandoned the religion which they learned, embrace another of any kind, even Catholicism. This is certainly a monstrous impiety which assigns the same praise and the mark of the just and upright man to truth and to error, to virtue and to vice, to goodness and to turpitude. Indeed this deadly idea concerning the lack of difference among religions is refuted even by the light of natural reason. We are assured of this because the various religions do not often agree among themselves. If one is true, the other must be false; there can be no society of darkness with light. Against these experienced sophists the people must be taught that the profession of the Catholic faith is uniquely true, as the apostle proclaims: one Lord, one faith, one baptism. Jerome used to say it this way: he who eats the lamb outside this house will perish as did those during the flood who were not with Noah in the ark. Indeed, no other name than the name of Jesus is given to men, by which they may be saved. He who believes shall be saved; he who does not believe shall be condemned.