Pope Pius XI —
"See to it, Venerable Brethren, that the Faithful do not allow themselves to be deceived! Communism is intrinsically evil..."
"In the beginning Communism showed itself for what it was in all its perversity, but very soon it realized that it was thus alienating the people. It has therefore changed its tactics and strives to entice the multitudes by trickery of various forms, hiding its real designs behind ideas that in themselves are good and attractive. Thus, aware of the universal desire for peace, the leaders of Communism pretend to be the most zealous promoters and propagandists in the movement for world amity. Yet at the same time they stir up a class warfare that causes rivers of blood to flow and, realizing that their system offers no internal guarantee of peace, they have recourse to unlimited armaments.
Under various names that do not suggest Communism, they establish organizations and periodicals with the sole purpose of carrying their ideas into quarters otherwise inaccessible. They try perfidiously to worm their way even into professedly Catholic and other religious organizations.Again, without receding an inch from their subversive principles, they invite Catholics to collaborate with them in the realm of so-called humanitarianism and charity; at times they even make proposals that are in perfect harmony with the Christian spirit and the doctrine of the Church.
Elsewhere they carry their hypocrisy so far as to encourage the belief that Communism, in countries where faith and culture are most strongly entrenched, will assume another and much milder form. 'It will not interfere with the practice of religion. It will respect liberty of conscience.'There are some even who refer to certain changes recently introduced into Soviet legislation as a proof that communism is about to abandon its program of war against God.
See to it Venerable Brethren, that the faithful do not allow themselves to be deceived! Communism is intrinsically wrong, and no one who would save Christian civilization may collaborate with it in any undertaking whatsoever. Those who permit themselves to be deceived into lending their aid toward the triumph of Communism in their own country will be the first to fall victims of their error. And the greater antiquity and grandeur of the Christian civilization in the regions where communism successfully penetrates, so much more devastating will be the hatred displayed by the godless."
Divini Redemptoris is an encyclical of Pope Pius XI (1922-1939) published in 1937, pointing out errors of communism, notably:
1) Its atheistic materialism,
2) Its doctrine of class-war,
3) Its denial of the rights and liberties of the human person.