Pius XI had foreseen and condemned Assisi

Never, perhaps, in the past, have the minds of men been seized as hard as we see them today, of the desire to strengthen and extend for the common good of human society the fraternal relations which bind us together. because of our community of origin and nature.

The people, in fact, do not yet fully enjoy the benefits of peace; and even, here and there, old and new discords provoke the eruption of seditions and civil wars. Moreover, most, certainly, controversies that affect the tranquility and prosperity of peoples can not in any way receive a solution without the concerted action and efforts of Heads of States and those who manage and pursue them. the interests. It is therefore easy to understand, and all the more so because no one refuses to admit the unity of the human race, why most men wish to see, in the name of this universal fraternity, the various peoples uniting with each other by links each day closer.

It is a similar result that some strive to obtain in things that look at the new order of the Law, brought by Christ our Lord. Convinced that it is very rare to meet men devoid of any religious meaning, we see them harboring the hope that it would be possible to bring without difficulty the peoples, despite their religious differences, to a fraternal understanding of the profession. certain doctrines considered as a common foundation of spiritual life.

Therefore, they begin to hold congresses, meetings, conferences attended by a significant number of listeners, and, in their discussions, they invite all men indiscriminately, the infidels of all kinds as the faithful of the Christ, and even those who, unfortunately, have separated from Christ or who, with bitterness and obstinacy, deny the divinity of his nature and his mission.

Such enterprises can not, in any way, be approved by Catholics , since they are based on the erroneous theory that religions are all more or less good and praiseworthy, in the sense that all too, although in different ways manifest and signify the natural and innate feeling that leads us to God and urges us to respectfully acknowledge His power. In truth, the partisans of this theory go astray in error, but moreover, by perverting the notion of the true religion they repudiate it, and they pour in stages in naturalism and atheism.

The conclusion is clear: to join the partisans and propagators of such doctrines is to move away completely from divinely revealed religion.

His Holiness Pope Pius XI - Encyclical Mortalium animos (1928)