2 For these reasons, therefore, the fatherly love We bear to all the nations of the world, and which impelled Us to recall the peoples of Ireland, Spain, and Italy to their duty, when the need arose, by Our letters to their Bishops - has induced Us to turn Our attention and thought to France. The designs of which We have just spoken are injurious, not only to religion, but are also harmful and fatal to the State; for it is impossible that prosperity should follow a State in which the influence of religion is extinguished. The moment man ceases to be in fear of God, he is deprived of the most necessary basis of justice, without which - even in the opinion of the Pagan philosophers-society cannot exist; the authority of rulers will lose its weight, and the laws of the land their force. Self-interest will weigh more with every man than high principles, and the integrity of rights will be threatened, for the fear of punishment is but a bad guarantee for the fulfilment of duty; those who rule will easily be led to exceed the proper limits of their authority, and those who obey seduced into sedition and revolt. Moreover, as there is nothing good in nature which is not to be referred to the Divine goodness, every human society which does its utmost to exclude God from its laws and its constitution, rejects the help of this Divine beneficence, and deserve, also, that help should be denied it. Rich, therefore, and powerful as it appears, that society bears within itself the seeds of death, and cannot hope for a lengthy existence. It is, indeed, with Christian peoples as with individuals; it is safety to follow the counsels of God, it is danger to fall away from them; and it often happens that when nations jealously retain their fidelity to God and the Church, they arrive, almost naturally, at the highest pitch of natural prosperity; but that when they fall away from it they perish. These facts are to be found in history; and We could cite to you more recent instances, even in your own country, had We the time to recall the events seen by a previous generation, when the impiety of the mob shook France to its very foundations, and Church and State perished in the same destruction. But, on the other hand, these certain causes of the State's ruin are easily removed, if, in the constitution and ruling of the family and of society, the precepts are observed of the Catholic religion, for these are most eminently fitted to preserve order and the welfare of the State.
Source: Nobilissima Gallorum Gens (Vatican.va)