24 But We, on the other hand, Venerable Brethren, in virtue of Our pastoral office, must bear aloft these names and these ideas, and preserve them in their true meaning, in their genuine dignity, and still more in their practical and necessary application to Christian life. To this We are urged by the very defense of God and Religion, which We sustain, since penance is of its nature a recognition and a re-establishment of the moral order in the world which is founded on the eternal law, that is on the living God. He who makes satisfaction to God for sin, recognizes thereby the sanctity of the highest principles of morality, their internal binding power, the need of a sanction against their violation. Certainly one of the most dangerous errors of our age is the claim to separate morality from religion, thus removing all solid basis for any legislation. This intellectual error might perhaps have passed unnoticed and appeared less dangerous when it was confined to a few, and belief in God was still the common heritage of mankind, and was tacitly presumed even in the case of those who no longer professed it openly. But today, when atheism is spreading through the masses of the people, the practical consequences of such an error become dreadfully tangible, and realities of the saddest kind make their appearance in the world. In place of moral laws, which disappear together with the loss of faith in God, brute force is imposed, trampling on every right. Old time fidelity and honesty of conduct and mutual intercourse extolled so much even by the orators and poets of paganism, now give place to speculations in one's own affairs as in those of others without reference to conscience. In fact, how can any contract be maintained, and what value can any treaty have, in which every guarantee of conscience is lacking? And how can there be talk of guarantees of conscience, when all faith in God and all fear of God has vanished? Take away this basis, and with it all moral law falls, and there is no remedy left to stop the gradual but inevitable destruction of peoples, families, the State, civilization itself.
Source: Caritate Christi Compulsi (Vatican.va)