The Church alone, being the Bride of Christ and having all things in common with her Divine Spouse, is the depository of the truth.
Pope Pius XIt is an error to believe that Christ did not teach a determined body of doctrine applicable to all times and to all men, but rather that He inaugurated a religious movement adapted, or to be adapted, to different times and different places.
Pope Pius XIs it permitted for Catholics to be present at, or to take part in, conventions, gatherings, meetings, or societies of non-Catholics which aim to associate together under a single agreement everyone who, in any way, lays claim to the name of Christian? In the negative! ... It is clear, therefore, why this Apostolic See has never allowed its subjects to take part in the assemblies of non-Catholics. There is one way in which the unity of Christians may be fostered, and that is by furthering the return to the one true Church of Christ for those who are separated from Her.
Pope Pius XTo heal the breach between the rich and the poor, it is necessary to distinguish between justice and charity.
Pope Pius XOur Apostolic Mandate requires from Us that We watch over the purity of the Faith and the integrity of Catholic discipline. It requires from Us that We protect the faithful from evil and error; especially so when evil and error are presented in dynamic language which, concealing vague notions and ambiguous expressions with emotional and high-sounding words, is likely to set ablaze the hearts of men in pursuit of ideals which, whilst attractive, are nonetheless nefarious.
Pope Pius X