Apologeticae sive Theologiae Fundamentalis, Tomus II (Pars Altera): Demonstratio Catholica

Those adversaries who admit that the Church will indeed endure perpetually nevertheless contend that it has been essentially changed or can be changed. The Fraticelli "spirituales", condemned by John XXII, asserted that the gospel had been concealed in the Church until now, indeed wholly extinguished.¹ The Reformers contended that the Church under the supreme pontiffs had been so foully corrupted and collapsed that scarcely its ruins remained.² Following in Protestant footsteps, the Jansenists and the Synod of Pistoia reproached the Church for having "grown old" and obscured nearly all its doctrines.³ To these are added the Modernists, lamenting a spirit of the "curia" hostile to reforms and demanding that the Church conform and adapt itself in all things to the ideas of present-day liberalism.

Catholics, on the contrary, have always held and hold that those things which are of human institution in the Church can indeed be changed according to the various necessities of the times, the essence of the Church instituted by Christ Himself remaining nevertheless unharmed.⁴ This immutability of the Church follows from its perpetuity, its end, its promise, and its infallibility.

1. From the perpetuity of the Church, or its indefectible existence. For the dogma must be applied to the Church: "Let it be, as it is, or let it not be." A Church essentially changed would no longer be the Church of Christ. Hence at the very moment at which the Church would fail with respect to essence, it would already have failed with respect to existence. But, from what has been said, it is indefectible with respect to existence; therefore it is also indefectible with respect to essence.

2. From the end of the Church. The proximate end of the Church consists in this, that through it the work of redemption be rendered perennial, i. e. that the Christian religion be preserved and administered; the remote end of the Church, however, consists in this, that in it and through it men may be saved, i. e. may attain eternal life. It is evident, moreover, that both the one and the other end would be impossible of attainment if the Church were essentially corrupted.

3. From the promise of the Church. For Christ promised the Church so great a stability that the gates of hell shall not prevail against it.⁵ But the gates of hell would altogether prevail against the Church if they corrupted it essentially. Moreover, Christ promised that He would be with the Church even to the end of the world: "Behold, I am with you all days even to the consummation of the world."⁶ But the assistance of Christ must most efficaciously prevent the Church from failing in its essence.

4. From the infallibility of the Church. In the second section of the Catholic demonstration we shall show that Christ instituted in His Church an infallible magisterium, which neither errs nor can err concerning the deposit of revelation, i. e. concerning all those things which are of the essence of the Christian religion. But since the Church adheres, and must necessarily adhere, to this magisterium, it is itself rendered infallible. Whence it cannot be changed or corrupted.