The underlying principle of these new opinions [Americanism] is that, in order to more easily 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, [discipline] 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. The Vatican Council [Vatican I] says concerning this point: “For the doctrine of faith which God has revealed has not been proposed, like a philosophical invention to be perfected by human ingenuity, but has been delivered as a divine deposit to the Spouse of Christ to be faithfully kept and infallibly declared. Hence that meaning of the sacred dogmas is perpetually to be retained which our Holy Mother, the Church, has once declared, nor is that meaning ever to be departed from under the pretense or pretext of a deeper comprehension of them.” – Constitutio de Fide Catholica, Chapter iv. [Which I couldn’t find on the Vatican website.]
Oddly, Testem benevolentiae is NOT listed on the Vatican website among the encyclicals or apostolic letters of this great, undervalued Pope. HERE
One must wonder…. why?