"IMMORTALE DEI". - It is one of the great encyclicals of Leo XIII (19 Nov. 1885), in which, taking up again the principles of Gregory XVI (encyclical Mirari vos) and Pius IX (Syllabus, encyclical Quanta cura), he fixes the doctrine on the reciprocal rights and duties of Church and State and on the freedoms claimed by modern peoples, and above all fixes for the first time the limits within which Catholics may lend themselves to the claims of peoples and to the pretensions of the State.
Already to the ideas set forth at the Congress of Malines (1863) by the liberal Catholics, the supreme pontiff Pius IX had given a reserved and private-form reply by means of a letter of Card. Antonelli: this clarification, however, did not in the least slow the expansion and the threat of liberalism. A new condemnation was demanded by the circumstances themselves. The encyclical Quanta cura of 8 Dec. 1864 admirably accomplishes this task: the liberal ideas were reproved with such clarity that even their own supporters had to abandon the struggle on the basis of the equivocation. The error was placed in its true light, with the explicit condemnation of naturalism; yet the liberal tendencies were not entirely extinguished, and they continued here and there in speeches, in newspapers, in reviews. Though without having the appearance of a doctrinal system, in almost all the European nations these ideas provoked dissensions among Catholics. Leo XIII with the encyclical Nobilissima Gallorum gens (1884) deplored these pernicious divisions bound up with bitter polemics and invited the faithful to unite for the defense of the greater interests of religion. In the same spirit he wrote to the Spanish bishops (Cum multa sint, 1884) so that the religious question might not be confused with the dynastic contests between Carlists and partisans of the constitution. This appeal was not favorably received. Moreover in France the Univers did not cease to criticize the practical tendencies of the new Pontiff: in Spain the Siglo censured the manner of acting of the nuncio and of the Holy See. In Rome itself the ideas of conciliation were attacked. The articles that appeared in Spain and in Rome were openly disapproved by the Holy See. Card. Pitra, however, when questioned on the import of this disapproval, replied with a defense of the censured authors. To put an end to all these disputes and divisions, Leo XIII intervened with a doctrinal document: the encyclical I. D., which sets forth the fundamental principles governing the relations between the modern Catholic State and the Church. One of the unifying elements of the State is authority, which, although it cannot come from any source other than God (Rom. 13, 2), nevertheless expresses itself in various forms of government, which, if they follow the law of divine justice, cannot be reproved by the Church. To this divine origin there corresponds for peoples the obligation of submission to legitimate authority, without recourse to revolt (Rom. 13, 2). This obligation is founded on the natural law that impels man toward society and toward the due reverence for the divine Majesty. It is an obligation of religion that must be felt not by the individual alone, but also by the whole of society, which can in no way act as if God did not exist, but must favor the true religion in every way. Between the two societies, therefore, each sovereign in its own jurisdiction, there must reign not struggle but harmony; moreover the ultimate and remote end of the one and of the other perfect society coincide: to attain the true good of humanity. This concord, the supreme law of the Middle Ages, has been broken by the atheistic State, by unlimited freedom of thought, of speech, of the press and by the absolute equality of all cults, with pernicious consequences for the formation of youth and of peoples. From this, however, it does not follow that the Church is an enemy of progress and repudiates the modern State, since she has always been the standard-bearer of the development of every cultural and social form that has for its end the general well-being; she rejects only the doctrines that under the pretext of freedom open to peoples the way of every license and of servitude. In particular the freedom of cults can be tolerated only in view of a greater good that may come from it to the Church. The ecclesiastical authority has never condemned free discussion on purely political problems. The conduct of Catholics, however, in such questions must always conform to the directives of the Holy See and of the bishops.