«MORTALIUM ANIMOS». – Opening words of the encyclical letter of Pius XI of 6 January 1928 De vera religionis unitate fovenda (AAS, 20 [1928], pp. 5–16), published almost immediately after the Lausanne Conference (3–21 August 1927) and the negative response of the Congregation of the Holy Office to the question whether Catholics might lawfully participate in pan-Christian congresses (8 July 1927, in AAS, 19 [1927], p. 278). In opposition, in fact, to the attitude of the Catholic Church, steadfast in its principles, there was gaining ground, after the pan-Christian Conferences of Stockholm and Lausanne, the conception of a Catholicism of broader scope, a kind of alliance between the Church of Rome and the other separated Christian communities, with the aim of opposing the universal brotherhood of the disciples of Jesus to the invading forces of unbelief.
The encyclical is the Church’s position against this new conception, and is divided into three parts. In the first, the Pontiff points out the fact that men desire to unite among themselves, a desire that assumes three different forms: the union of all men as possessing the same common origin and nature, as the basis and guarantee of cooperation and peace—an eminently desirable union; the union of all men who have a religion, whatever it may be, as a barrier against impiety and irreligion—a form of union that Catholics cannot so simply support; and the union of all Christians, or pan-Christianism. It is this third form that the Pontiff intends to discuss. In the second part, it is affirmed that by natural and divine-positive law the only true religion is the Christian-Catholic religion, and that Jesus founded one Church alone as a visible and sovereign society destined to gather all men into its bosom. Consequently, the Pope denounces the error of those who view the Church merely as a federation of communities; who assert that the Lord’s desire for one flock has not yet been realized, as though the true Church of Jesus Christ did not yet exist or existed without a Shepherd; and who aspire to a practical union with Rome, the result of compromises and mutual concessions. In the third part, Pius XI affirms that consequently neither the Holy See nor Catholics can take part in or encourage these movements, insofar as they «falsae cuidam christianae religionis auctoritatem adiungeren». Nor is this contrary to charity, because true charity cannot be opposed to truth and faith. The exclusion of a single magisterium that would constitute an obligation for all is a factor of disintegration, not of union, and opens the way to indifferentism. The discrimination between fundamental and non-fundamental truths, with a lesser obligation regarding the latter (v. JANNI, 1920), when revealed truths are concerned, is meaningless. True union is therefore possible only through the return of dissidents to the true Church and through acceptance of the primacy of St. Peter and his successors. The encyclical, which was published in circumstances analogous to those in which Leo XIII published Satis cognitum in 1896, is less extensive than its predecessor; nevertheless, it reveals a sense of resolve in affirming the Church’s doctrine in the face of the deliberately elastic statements, full of cautious reticence, made by the Conferences of Stockholm and Lausanne. That resolve, although it may at first seem an obstacle to the return of the separated brethren, because it excludes any opening to dangerous equivocation, represents a step forward—one that may seem short, but is sure.