The underlying principle of these new opinions [he is speaking of Americanism] is that, in order the more easily to attract those who differ from her, the Church should shape her teachings more in accord with the spirit of the age and relax some of her ancient severity and make some concessions to new opinions. Many think that these concessions should be made not only in regard to ways of living, but even in regard to doctrines which belong to the deposit of the faith. They contend that it would be opportune, in order to gain those who differ from us, to omit certain points of her teaching which are of lesser importance, and to tone down the meaning which the Church has always attached to them. It does not need many words, beloved son, to prove the falsity of these ideas if the nature and origin of the doctrine which the Church proposes are recalled to mind. … Let it be far from anyone’s mind to suppress for any reason any doctrine that has been handed down. Such a policy would tend rather to separate Catholics from the Church than to bring in those who differ. (Testem Benevolentiae)
Can papal writing get clearer than this? That which belongs to the doctrine of faith and morals handed down by the Church is immutable, unassailable, always relevant, always required; it is from God as its author, for God as its final end, within man’s power by the help of God’s grace—and by it every man will be judged, for God is no respecter of persons.
The intellectuals of modernity have their own inextinguishable fantasies. For them, remaining the same is bad; preserving the same truths, handing down the same faith, practicing the same rituals and devotions, calling the same things by the same names—all this is a sign of stagnation, introversion, retreat, imbecility. What is needed is to crank up the Hegelian dialectic and confront every traditional thesis with its modern antithesis, in order to bring forth the new and improved religion of the day, “Christian on the outside, modern on the inside!”
It is part of the Church’s job, not the most glamorous but perhaps the most necessary, to pierce these dreamy bubbles and lead men back to their senses and their responsibilities. Cardinal Ratzinger said it with his customary forcefulness: “The mythic luster attached to concepts such as change and revolution must be demythologized.”
When I think of classic authors who can remind us of the real nature of Christianity, my favorite would certainly be St. Vincent of Lérins (d. ca. 445), who comments on Galatians 1:8, “But though we, or an angel from heaven, preach a gospel to you besides that which we have preached to you, let him be anathema”:
To announce to Catholic Christians a doctrine other than that which they have received was never permitted, is nowhere permitted, and never will be permitted. It was ever necessary, is everywhere necessary, and ever will be necessary that those who announce a doctrine other than that which was received once and for all be anathema. If this be so, is there anyone alive so bold or so foolish as to accept doctrines besides those accepted by the Church? Crying aloud, crying aloud again and again and again, crying aloud to everyone, always and everywhere throughout his writings, is he, this vessel of election, this doctor of the Gentiles, this trumpet among the Apostles, this herald of the earth, this heaven-conscious man; he is crying aloud that whoever announces a new doctrine is anathema. (Commonitories, ch. 9)