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 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 XWhat will it cost you, oh Mary, to hear our prayer? What will it cost you to save us? Has not Jesus placed in your hands all the treasures of His grace and mercy? You sit crowned Queen at the right hand of your son: your dominion reaches as far as the heavens and to you are subject the earth and all creatures dwelling thereon. Your dominion reaches even down into the abyss of hell, and you alone, oh Mary, save us from the hands of Satan.
Pope Pius X...the great movement of apostasy being organized in every country for the establishment of a One-World Church which shall have neither dogmas, nor hierarchy, neither discipline for the mind, nor curb for the passions, and which, under the pretext of freedom and human dignity, would bring back to the world (if such a Church could overcome) the reign of legalized cunning and force, and the oppression of the weak, and of all those who toil and suffer. [...] Indeed, the true friends of the people are neither revolutionaries, nor innovators: they are traditionalists.
Pope Pius XBut since the Modernists (as they are commonly and rightly called) employ a very clever artifice, namely, to present their doctrines without order and systematic arrangement into one whole, scattered and disjointed one from another, so as to appear to be in doubt and uncertainty, while they are in reality firm and steadfast, it will be of advantage, Venerable Brethren, to bring their teachings together here into one group, and to point out the connexion between them, and thus to pass to an examination of the sources of the errors, and to prescribe remedies for averting the evil.
Pope Pius X