All Catholics must make themselves felt as active elements in daily political life in the countries where they live. They must penetrate, wherever possible, in the administration of civil affairs; must constantly exert the utmost vigilance and energy to prevent the usages of liberty from going beyond the limits fixed by God's law. All Catholics should do all in their power to cause the constitutions of states and legislation to be modeled on the principles of the true Church.
Pope Leo XIIIThese most crafty enemies [the devils] have filled and inebriated with gall and bitterness the Church, the spouse of the Immaculate Lamb, and have laid impious hands on Her most sacred possessions. In the Holy Place itself, where has been set up the See of the most holy Peter and the Chair of Truth for the light of the world, they have raised the throne of their abominable impiety, with the iniquitous design that when the Pastor has been struck, the sheep may be scattered.
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 XIIIHence 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 XIIIThe Eucharist is source and pledge of blessedness and glory, not for the soul alone, but for the body also.... In the frail and perishable body that divine Host, which is the immortal body of Christ, implants a principle of resurrection, a seed of immortality, which one day must germinate
Pope Leo XIII