«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 Aug. 1927) and the negative response of the Congregation of the Holy Office to the doubt whether it is lawful for Catholics to take part 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 with a broader outlook, a kind of alliance between the Church of Rome and the other separated Christian communities, with the aim of opposing the spreading unbelief with the universal brotherhood of the disciples of Jesus.
The encyclical is a statement of the Church’s position against this new conception; it is divided into three parts. In the first, the Pontiff notes the fact of mankind’s desire to unite, a desire that takes three different forms: union of all men as sharing the same common origin and nature, as a basis and guarantee of collaboration and peace, a union truly to be desired; union of all men who have a religion, whatever it may be, as a barrier against impiety and irreligion: a similar form of union cannot simply be supported by Catholics; union of all Christians or pan-Christianism. It is this third form that the Pontiff wishes to address. In the second part, it is affirmed that by natural and divinely positive right the only true religion is the Christian-Catholic religion, and that Jesus founded a single Church as a visible and sovereign society destined to gather all men within its bosom. Consequently, the Pope denounces the error of those who see the Church only as a federation of communities; who affirm that the Lord’s desire for one fold has not yet been able to be realised, as if the true Church of Jesus Christ did not exist or existed without a Shepherd; who aspire to a practical union with Rome, resulting from compromises and mutual concessions. In the third part, Pius XI affirms that consequently neither the Holy See nor Catholics can believe in or favour these movements inasmuch as they would «falsae cuidam christianae religioni auctoritatem adiungerent». Nor is this contrary to charity, because true charity cannot be against truth and faith. The exclusion of a single magisterium that would constitute an obligation for all is a factor of disintegration rather than of union and opens the way to indifferentism. The distinction between fundamental and non-fundamental truths with a lesser commitment to the latter (v. JANNI, UCO, Ugo), when it comes to revealed truths, makes no sense. True union is therefore possible only with the return of the dissidents to the true Church and with the 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 the previous one; yet it reveals a sense of decisiveness in affirming the doctrine of the Church in the face of the deliberately elastic declarations and full of cautious reticence of the conferences of Stockholm and Lausanne. This decisiveness, if it may at first impression seem an obstacle to the return of the separated brethren, by the fact that it excludes any dangerous misunderstanding, represents an advance, which may seem small, but is sure.