57 On this point We have already insisted in Our Allocution of May 12th of last year, but We believe it to be a duty of special urgency, Venerable Brethren, to call your attention to it once again. 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 which 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 which 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 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; and at times 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 more 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.
Source: Divini Redemptoris (Vatican.va)