Hence from all we have hitherto said, it is clear beloved Catholics that we cannot approve the opinions which some [Protestants, Jews, and other heretics] comprise under the head of Americanism [freedom].
Pope Leo XIIIThere is in the Sacred Heart the symbol and express image of the infinite love of Jesus Christ which moves us to love in return.
Pope Leo XIIIRemember and understand well that where Peter is, there is the Church; that those who refuse to associate in communion with the Chair of Peter belong to Antichrist, not to Christ. He who would separate himself from the Roman Pontiff has no further bond with Christ.
Pope Leo XIIIThe first law of history is to dread uttering a falsehood; the next is not to fear stating the truth; lastly, the historian's writings should be open to no suspicion of partiality or animosity.
Pope Leo XIIIThe sacred rites, although not instituted specifically for proving the truth of the dogmas of the Catholic Faith incontrovertibly, are effectively the living voice of Catholic Truth, the oft-sounded expression of it. For that very reason the true Church of Christ, even as she shows great zeal to guard inviolate those forms of divine worship - since they are hallowed and are not to be changed - sometimes grants or permits something novel in the performance of them in certain instances. This she does especially when they are in conformity with their venerable antiquity.
Pope Leo XIII