If Socialism, like all errors, contains some truth (which, moreover, the Supreme Pontiffs have never denied), it is based nevertheless on a theory of human society peculiar to itself and irreconcilable with true Christianity. Religious socialism, Christian socialism, are contradictory terms; no one can be at the same time a good Catholic and a true socialist.
Pope Pius XIFor what will it profit men that a more prudent distribution and use of riches make it possible for them to gain even the whole world, if thereby they suffer the loss of their own souls? What will it profit to teach them sound principles in economics, if they permit themselves to be so swept away by selfishness, by unbridled and sordid greed, that hearing the commandments of the Lord, they do all things contrary.
Pope Pius XI"Religious Socialism," "Christian Socialism," are expressions implying a contradiction in terms.
Pope Pius XIWhether considered as a doctrine, or as an historical fact, or as a movemement, socialism, if it really remains socialism, cannotbe brought into harmony with the dogmas of the Catholic church.... Religious socialism, Christian socialism, are expressions implying a contradiction in terms.
Pope Pius XIAlways moved by religious motives, the Church has condemned the various forms of Marxist Socialism; and she condemns them today, because it is her permanent right and duty to safeguard men from currents of thought and influence that jeopardize their eternal salvation.
Pope Pius XIThis organic conception of society, the only vital conception, combines a noble humanism with the genuine Christian spirit, and it bears the inscription from Holy Writ which St. Thomas has explained: "The work of justice shall be peace"; a text applicable to the life of a people whether it be considered in itself or in its relations with other nations.
Pope Pius XI