MIRARI VOS

DsZ 2370 (13.) Now We consider another abundant source of the evils with which the Church is afflicted at present: indifferentism. This perverse opinion is spread on all sides by the fraud of the wicked who claim that it is possible to obtain the eternal salvation of the soul by the profession of any kind of religion, as long as morality is maintained......(14.) This shameful font of indifferentism gives rise to that absurd and erroneous proposition which claims that liberty of conscience must be maintained for everyone.

DsZ 2371 (14) It spreads ruin in sacred and civil affairs, though some repeat over and over again with the greatest impudence that some advantage accrues to religion from it. "But the death of the soul is worse than freedom of error," as Augustine was wont to say.[21] When all restraints are removed by which men are kept on the narrow path of truth, their nature, which is already inclined to evil, propels them to ruin. Then truly "the bottomless pit"[22] is open from which John saw smoke ascending which obscured the sun, and out of which locusts flew forth to devastate the earth. Thence comes transformation of minds, corruption of youths, contempt of sacred things and holy laws -- in other words, a pestilence more deadly to the state than any other. Experience shows, even from earliest times, that cities renowned for wealth, dominion, and glory perished as a result of this single evil, namely immoderate freedom of opinion, license of free speech, and desire for novelty.

DsZ 2372 (22) The first to be embraced with paternal affection are those who apply themselves to the sacred sciences and to philosophical studies. For them may you be exhorter and supporter, lest trusting only in their own talents and strength, they may imprudently wander away from the path of truth onto the road of the impious. Let them remember that God is the guide to wisdom and the director of the wise.[31] It is impossible to know God without God who teaches men to know Himself by His word.[32]