Is 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 XTruly we are passing through disastrous times, when we may well make our own the lamentation of the Prophet: "There is no truth, and there is no mercy, and there is no knowledge of God in the land" (Hosea 4:1). Yet in the midst of this tide of evil, the Virgin Most Merciful rises before our eyes like a rainbow, as the arbiter of peace between God and man.
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 XWe put great confidence in the Holy Rosary for the healing of evils which afflict our times.
Pope Pius XIt is impossible to approve in Catholic publications of a style inspired by unsound novelty which seems to deride the piety of the faithful and dwells on the introduction of a new order of Christian life, on new directions of the Church, on new aspirations of the modern soul, on a new vocation of the clergy, on a new Christian civilisation.
Pope Pius X