The following excerpts are taken from Pope Leo XIII's encyclical Immortale Dei. Here he addresses in quite some detail the problems pertaining to the Church and State, and the related question of religious liberty. In these days, several errors have sprung up with regard to these matters, and a false religious liberty is held up and esteemed as an ideal towards which to work. Pope Leo here explains why this is false. I think there is even a case to be made, based on these words, for how this false notion of religious freedom is actually responsible for the oppression of the Catholic Church by the State which we experience today. It is ironic that the very cause of this problem is being proposed as the remedy...
6... [T]he State, constituted as it is, is clearly bound to act up to the manifold and weighty duties linking it to God, by the public profession of religion. Nature and reason, which command every individual devoutly to worship God in holiness, because we belong to Him and must return to Him, since from Him we came, bind also the civil community by a like law. For, men living together in society are under the power of God no less than individuals are, and society, no less than individuals, owes gratitude to God who gave it being and maintains it and whose ever-bounteous goodness enriches it with countless blessings. Since, then, no one is allowed to be remiss in the service due to God, and since the chief duty of all men is to cling to religion in both its teaching and practice - not such religion as they may have a preference for, but the religion which God enjoins, and which certain and most clear marks show to be the only one true religion - it is a public crime to act as though there were no God. So, too, is it a sin for the State not to have care for religion as a something beyond its scope, or as of no practical benefit; or out of many forms of religion to adopt that one which chimes in with the fancy; for we are bound absolutely to worship God in that way which He has shown to be His will. All who rule, therefore, would hold in honour the holy name of God, and one of their chief duties must be to favour religion, to protect it, to shield it under the credit and sanction of the laws, and neither to organize nor enact any measure that may compromise its safety. This is the bounden duty of rulers to the people over whom they rule. For one and all are we destined by our birth and adoption to enjoy, when this frail and fleeting life is ended, a supreme and final good in heaven, and to the attainment of this every endeavour should be directed. Since, then, upon this depends the full and perfect happiness of mankind, the securing of this end should be of all imaginable interests the most urgent. Hence, civil society, established for the common welfare, should not only safeguard the well-being of the community, but have also at heart the interests of its individual members, in such mode as not in any way to hinder, but in every manner to render as easy as may be, the possession of that highest and unchangeable good for which all should seek. Wherefore, for this purpose, care must especially be taken to preserve unharmed and unimpeded the religion whereof the practice is the link connecting man with God...
13...The Almighty, therefore, has given the charge of the human race to two powers, the ecclesiastical and the civil, the one being set over divine, and the other over human, things. Each in its kind is supreme, each has fixed limits within which it is contained, limits which are defined by the nature and special object of the province of each, so that there is, we may say, an orbit traced out within which the action of each is brought into play by its own native right. But, inasmuch as each of these two powers has authority over the same subjects, and as it might come to pass that one and the same thing-related differently, but still remaining one and the same thing-might belong to the jurisdiction and determination of both, therefore God, who foresees all things, and who is the author of these two powers, has marked out the course of each in right correlation to the other. "For the powers that are, are ordained of God."! Were this not so, deplorable contentions and conflicts would often arise, and, not infrequently, men, like travellers at the meeting of two roads, would hesitate in anxiety and doubt, not knowing what course to follow. Two powers would be commanding contrary things, and it would be a dereliction of duty to disobey either of the two...
21. There was once a time when States were governed by the philosophy of the Gospel. Then it was that the power and divine virtue of Christian wisdom had diffused itself throughout the laws, institutions, and morals of the people, permeating all ranks and relations of civil society. Then, too, the religion instituted by Jesus Christ, established firmly in befitting dignity, flourished everywhere, by the favour of princes and the legitimate protection of magistrates; and Church and State were happily united in concord and friendly interchange of good offices. The State, constituted in this wise, bore fruits important beyond all expectation, whose remembrance is still, and always will be, in renown, witnessed to as they are by countless proofs which can never be blotted out or ever obscured by any craft of any enemies. Christian Europe has subdued barbarous nations, and changed them from a savage to a civilized condition, from superstition to true worship. It victoriously rolled back the tide of Mohammedan conquest; retained the headship of civilization; stood forth in the front rank as the leader and teacher of all, in every branch of national culture; bestowed on the world the gift of true and many-sided liberty; and most wisely founded very numerous institutions for the solace of human suffering. And if we inquire how it was able to bring about so altered a condition of things, the answer is-beyond all question, in large measure, through religion, under whose auspices so many great undertakings were set on foot, through whose aid they were brought to completion.
22. A similar state of things would certainly have continued had the agreement of the two powers been lasting. More important results even might have been justly looked for, had obedience waited upon the authority, teaching, and counsels of the Church, and had this submission been specially marked by greater and more unswerving loyalty. For that should be regarded in the light of an ever-changeless law which No of Chartres wrote to Pope Paschal II: "When kingdom and priesthood are at one, in complete accord, the world is well ruled, and the Church flourishes, and brings forth abundant fruit. But when they are at variance, not only smaller interests prosper not, but even things of greatest moment fall into deplorable decay."(21)
23. But that harmful and deplorable passion for innovation which was aroused in the sixteenth century threw first of all into confusion the Christian religion, and next, by natural sequence, invaded the precincts of philosophy, whence it spread amongst all classes of society. From this source, as from a fountain-head, burst forth all those later tenets of unbridled license which, in the midst of the terrible unheavals of the last century, were wildly conceived and boldly proclaimed as the principles and foundation of that new conception of law which was not merely previously unknown, but was at variance on many points with not only the Christian, but even the natural law.
24. Amongst these principles the main one lays down that as all men are alike by race and nature, so in like manner all are equal in the control of their life; that each one is so far his own master as to be in no sense under the rule of any other individual; that each is free to think on every subject just as he may choose, and to do whatever he may like to do; that no man has any right to rule over other men. In a society grounded upon such maxims all government is nothing more nor less than the will of the people, and the people, being under the power of itself alone, is alone its own ruler. It does choose, nevertheless, some to whose charge it may commit itself, but in such wise that it makes over to them not the right so much as the business of governing, to be exercised, however, in its name.
25. The authority of God is passed over in silence, just as if there were no God; or as if He cared nothing for human society; or as if men, whether in their individual capacity or bound together in social relations, owed nothing to God; or as if there could be a government of which the whole origin and power and authority did not reside in God Himself. Thus, as is evident, a State becomes nothing but a multitude which is its own master and ruler. And since the people is declared to contain within itself the spring-head of all rights and of all power, it follows that the State does not consider itself bound by any kind of duty toward God. Moreover, it believes that it is not obliged to make public profession of any religion; or to inquire which of the very many religions is the only one true; or to prefer one religion to all the rest; or to show to any form of religion special favour; but, on the contrary, is bound to grant equal rights to every creed, so that public order may not be disturbed by any particular form of religious belief.
26. And it is a part of this theory that all questions that concern religion are to be referred to private judgment; that every one is to be free to follow whatever religion he prefers, or none at all if he disapprove of all. From this the following consequences logically flow: that the judgment of each one's conscience is independent of all law; that the most unrestrained opinions may be openly expressed as to the practice or omission of divine worship; and that every one has unbounded license to think whatever he chooses and to publish abroad whatever he thinks.
27. Now, when the State rests on foundations like those just named - and for the time being they are greatly in favor - it readily appears into what and how unrightful a position the Church is driven. For, when the management of public business is in harmony with doctrines of such a kind, the Catholic religion is allowed a standing in civil society equal only, or inferior, to societies alien from it; no regard is paid to the laws of the Church, and she who, by the order and commission of Jesus Christ, has the duty of teaching all nations, finds herself forbidden to take any part in the instruction of the people. With reference to matters that are of twofold jurisdiction, they who administer the civil power lay down the law at their own will, and in matters that appertain to religion defiantly put aside the most sacred decrees of the Church. They claim jurisdiction over the marriages of Catholics, even over the bond as well as the unity and the indissolubility of matrimony. They lay hands on the goods of the clergy, contending that the Church cannot possess property. Lastly, they treat the Church with such arrogance that, rejecting entirely her title to the nature and rights of a perfect society, they hold that she differs in no respect from other societies in the State, and for this reason possesses no right nor any legal power of action, save that which she holds by the concession and favor of the government. If in any State the Church retains her own agreement publicly entered into by the two powers, men forthwith begin to cry out that matters affecting the Church must be separated from those of the State.
28. Their object in uttering this cry is to be able to violate unpunished their plighted faith, and in all things to have unchecked control. And as the Church, unable to abandon her chiefest and most sacred duties, cannot patiently put up with this, and asks that the pledge given to her be fully and scrupulously acted up to, contentions frequently arise between the ecclesiastical and the civil power, of which the issue commonly is that the weaker power yields to the one which is stronger in human resources.
29. Accordingly, it has become the practice and determination under this condition of public polity (now so much admired by many) either to forbid the action of the Church altogether, or to keep her in check and bondage to the State. Public enactments are in great measure framed with this design. The drawing up of laws, the administration of State affairs, the godless education of youth, the spoliation and suppression of religious orders, the overthrow of the temporal power of the Roman Pontiff, all alike aim to this one end - to paralyse the action of Christian institutions, to cramp to the utmost the freedom of the Catholic Church, and to curtail her ever single prerogative.
30. Now, natural reason itself proves convincingly that such concepts of the government of a State are wholly at variance with the truth. Nature itself bears witness that all power, of every kind, has its origin from God, who is its chief and most august source.
31. The sovereignty of the people, however, and this without any reference to God, is held to reside in the multitude; which is doubtless a doctrine exceedingly well calculated to flatter and to inflame many passions, but which lacks all reasonable proof, and all power of insuring public safety and preserving order. Indeed, from the prevalence of this teaching, things have come to such a pass that may hold as an axiom of civil jurisprudence that seditions may be rightfully fostered. For the opinion prevails that princes are nothing more than delegates chosen to carry out the will of the people; whence it necessarily follows that all things are as changeable as the will of the people, so that risk of public disturbance is ever hanging over our heads. To hold, therefore, that there is no difference in matters of religion between forms that are unlike each other, and even contrary to each other, most clearly leads in the end to the rejection of all religion in both theory and practice. And this is the same thing as atheism, however it may differ from it in name. Men who really believe in the existence of God must, in order to be consistent with themselves and to avoid absurd conclusions, understand that differing modes of divine worship involving dissimilarity and conflict even on most important points cannot all be equally probable, equally good, and equally acceptable to God.