The Origins of the Separation of Church and State

can be found in Christianity.  I got into a conversation with some SSPXers, got a bunch of links and resources out in the course of answering their challenges to this notion, and figured I might as well make them usefully available to more people.  So--here we go.

From Jesus Christ:

So Jesus said to them, “Repay to Caesar what belongs to Caesar and to God what belongs to God.” (Mark 12:17)

We get more in the New Testament letters.

Let every person be subordinate to the higher authorities, for there is no authority except from God, and those that exist have been established by God. Therefore, whoever resists authority opposes what God has appointed, and those who oppose it will bring judgment upon themselves. For rulers are not a cause of fear to good conduct, but to evil. Do you wish to have no fear of authority? Then do what is good and you will receive approval from it, for it is a servant of God for your good. But if you do evil, be afraid, for it does not bear the sword without purpose; it is the servant of God to inflict wrath on the evildoer. Therefore, it is necessary to be subject not only because of the wrath but also because of conscience. This is why you also pay taxes, for the authorities are ministers of God, devoting themselves to this very thing. Pay to all their dues, taxes to whom taxes are due, toll to whom toll is due, respect to whom respect is due, honor to whom honor is due. (Romans 13:1-7)

Be subject to every human institution for the Lord’s sake, whether it be to the king as supreme or to governors as sent by him for the punishment of evildoers and the approval of those who do good...Give honor to all, love the community, fear God, honor the king.(1 Peter 2:13-14, 17)

In none of these do we see any demand that the Church be supreme temporally over the rulers of the earth, and we see from the examples of the early Christian martyrs that the state, while having authority, has some very definite limits on its authority, a viewpoint which is summed up by St. Augustine:

An unjust law is no law at all. On Free Choice Of The Will, Book 1, § 5

When we see the Apostles before the Sanhedrin, they take the same stance:

But Peter and the apostles said in reply, “We must obey God rather than men..." (Acts 5:29)

UPDATE: And New Advent has this interesting piece of info.  Excerpts:

Though the Apostles were deeply imbued with the conviction that they must transmit the deposit of the Faith to posterity undefiled, and that any teaching at variance with their own, even if proclaimed by an angel of Heaven, would be a culpable offense, yet St. Paul did not, in the case of the heretics Alexander and Hymeneus, go back to the Old Covenant penalties of death or scourging (Deuteronomy 13:6 sqq.; 17:1 sqq.), but deemed exclusion from the communion of the Church sufficient (1 Timothy 1:20; Titus 3:10). In fact to the Christians of the first three centuries it could scarcely have occurred to assume any other attitude towards those who erred in matters of faith. Tertullian (To Scapula 2) lays down the rule:

Humani iuris et naturalis potestatis, unicuique quod putaverit colere, nec alii obest aut prodest alterius religio. Sed nec religionis est religionem colere, quae sponte suscipi debeat, non vi.

In other words, he tells us that the natural law authorized man to follow only the voice of individual conscience in the practice of religion, since the acceptance of religion was a matter of free will, not of compulsion. Replying to the accusation of Celsus, based on the Old Testament, that the Christians persecuted dissidents with death, burning, and torture, Origen (Against Celsus VII.26) is satisfied with explaining that one must distinguish between the law which the Jews received from Moses and that given to the Christians by Jesus; the former was binding on the Jews, the latter on the Christians. Jewish Christians, if sincere, could no longer conform to all of the Mosaic law; hence they were no longer at liberty to kill their enemies or to burn and stone violators of the Christian Law.
St. Cyprian of Carthage, surrounded as he was by countless schismatics and undutiful Christians, also put aside the material sanction of the Old Testament, which punished with death rebellion against priesthood and the Judges. "Nunc autem, quia circumcisio spiritalis esse apud fideles servos Dei coepit, spiritali gladio superbi et contumaces necantur, dum de Ecclesia ejiciuntur" (Epistle 61, no. 4) religion being now spiritual, its sanctions take on the same character, and excommunication replaces the death of the body. Lactantius was yet smarting under the scourge of bloody persecutions, when he wrote this Divine Institutes in A.D. 308. Naturally, therefore, he stood for the most absolute freedom of religion. He writes:

Religion being a matter of the will, it cannot be forced on anyone; in this matter it is better to employ words than blows [verbis melius quam verberibus res agenda est]. Of what use is cruelty? What has the rack to do with piety? Surely there is no connection between truth and violence, between justice and cruelty . . . . It is true that nothing is so important as religion, and one must defend it at any cost [summâ vi] . . . It is true that it must be protected, but by dying for it, not by killing others; by long-suffering, not by violence; by faith, not by crime. If you attempt to defend religion with bloodshed and torture, what you do is not defense, but desecration and insult. For nothing is so intrinsically a matter of free will as religion. (Divine Institutes V:20)

(/UPDATE)
The Christian teachers of the first three centuries insisted, as was natural for them, on complete religious liberty; furthermore, they not only urged the principle that religion could not be forced on others — a principle always adhered to by the Church in her dealings with the unbaptised — but, when comparing the Mosaic Law and the Christian religion, they taught that the latter was content with a spiritual punishment of heretics (i.e. with excommunication), while Judaism necessarily proceeded against its dissidents with torture and death.

Also, the flourishing of the early Church in the centuries before Constantine indicates that there is no necessary union between throne and altar in the Church's constitution.  Indeed, the witness of every young new branch of the Church, growing in new lands, indicates that the Church may endure without the protection or assistance of the earthly powers that be. For a discussion of the early Church's experience of the relations between Church and state, see Church and State in Early Christianity by Father Hugo Rahner, SJ (not the much-debated Karl Rahner, mind you, but his brother).

Later, we get a papal discussion of the objective superiority of the spiritual authority over the temporal, since it deals with the things of God rather than the passing things of this world. But in the letter Duo Sunt, Pope St. Gelasius still says that clerics rightly obey the laws of the Emperor, and recognize the authority of the rulers of the earth rightly. Excerpts:

Letter of Pope Gelasius to Emperor Anastasius on the superiority of the spiritual over temporal power: The pope's view of the natural superiority of the spiriitual over the temporal power finds a clear expression the following remarkable letter of Gelasius I (494).

There are two powers, august Emperor, by which this world is chiefly ruled, namely, the sacred authority of the priests and the royal power. Of these that of the priests is the more weighty, since they have to render an account for even the kings of men in the divine judgment. You are also aware, dear son, that while you are permitted honorably to rule over human kind, yet in things divine you bow your head humbly before the leaders of the clergy and await from their hands the means of your salvation. In the reception and proper disposition of the heavenly mysteries you recognize that you should be subordinate rather than superior to the religious order, and that in these matters you depend on their judgment rather than wish to force them to follow your will.

If the ministers of religion, recognizing the supremacy granted you from heaven in matters affecting the public order, obey your laws, lest otherwise they might obstruct the course of secular affairs by irrelevant considerations, with what readiness should you not yield them obedience to whom is assigned the dispensing of the sacred mysteries of religion. Accordingly, just as there is no slight danger m the case of the priests if they refrain from speaking when the service of the divinity requires, so there is no little risk for those who disdain - which God forbid -when they should obey. And if it is fitting that the hearts of the faithful should submit to all priests in general who properly administer divine affairs, how much the more is obedience due to the bishop of that see which the Most High ordained to be above all others, and which is consequently dutifully honored by the devotion of the whole Church.

Here's an overview of the development of the relationship between Church and state through the Middle Ages.

For more on the subject, see the work of Father John Courtney Murray, SJ, whose scholarship formed the basis of the decree Dignitatis Humanae, recognizing social and civil religious freedom as a right of the human person.  Excerpts from Weigel's discussion:

...When Murray began to work on the church-state problem in the mid-1940s, the regnant Roman theory -- which many simply identified with Catholic tradition tout court -- was that the preferred arrangement was state recognition of the prerogatives of the Catholic Church, and state support of the Church's work. In the Roman theological parlance of the time, this was the "thesis," and any other arrangement, like that in the United States, was a mere "hypothesis." This thesis/hypothesis schema was underwritten by another claim that many in Roman theological circles simply identified with Catholic "tradition": the claim that "error has no rights."

Unraveling this thick knot of seemingly settled "tradition" was no easy business, either intellectually or politically, in terms of stepping on ecclesiastical and theological toes. Murray's careful analysis of Leo XIII's texts suggested that the thesis/hypothesis business might not be as settled as it seemed. And, in a brilliant move, Murray reached beneath the thesis/hypothesis schema into a much older stratum of Catholic tradition, where he found, in the fifth-century writings of Pope Saint Gelasius I, a clear distinction between priestly authority and political authority -- which suggested that the conflation of those two authorities in the "thesis" was, in fact, not the Catholic tradition (a suggestion buttressed, of course, by reference to Christ's own distinction between what is Caesar's and what is God's in Matthew 22:21). Here was a true "liberal Catholicism" at work: a Catholicism that reached back into history to retrieve a long-forgotten element of the authentic tradition that, recovered, could be the engine of future development.

To make a long story short, Murray's work on religious freedom was vindicated at the Second Vatican Council. There, two compelling arguments came together in a powerful synthesis: Murray's historical work and his exegesis of Leo XIII, which put paid to the thesis/hypothesis schema, and European personalist philosophy, which showed the Council that, while "error" might have no rights (whatever that meant), persons had rights, whether their opinions were erroneous or not. That settled the question intellectually for most of the Council fathers. The politics of defining religious freedom as a basic human right were managed by another interesting coalition: Bishops from the Communist world, who wanted the Church to defend religious freedom so that they might use it as a new weapon in their own struggles, joined with U.S. bishops, who wanted the American constitutional arrangement vindicated, and Western European bishops, who were tired of ancien régime politics, formed a critical mass of support, resulting in Pope Paul VI's promulgation of Vatican II's landmark Declaration on Religious Freedom on December 7, 1965...

For more on the texts of Leo XIII in question, see here.  Excerpts:

 Leo XIII published a series of encyclicals on social and other questions which attracted universal attention. We may mention especially "Inscrutabilis" (21 April, 1878) on the evils of modern society; "Æterni Patris" (4 Aug., 1879) on St. Thomas Aquinas and Scholastic philosophy; "Arcanum divinæ sapientiæ" (10 Feb., 1880) on Christian marriage and family life; "Diuturnum illud" (29 June, 1881) on the origin of civil authority; "Immortale Dei" (1 Nov., 1885) on the Christian constitution of states; "Libertas præstantissimum" (20 June, 1888) on true liberty; "Rerum novarum" (16 May, 1891) on the labour question; "Providentissimus Deus" (18 Nov., 1893) on Holy Scripture; "Satis cognitum" (29 June, 1896) on religious unity.

The Declaration makes clear that it does not oppose the traditional condemnations of indifferentism or of the notion that humans have absolute freedom to choose to believe whatever they want without regard for truth or revelation. Rather, the view of religious freedom which they endorse is that the "social and civil" authorities have no right to compel citizens to profess beliefs or perform worship in which they do not believe, which goes against their consciences.  In other words, the force that may be applied to any person when it comes to matters of faith is the force of reason and grace--not physical coercion or the force of human law. Excerpts:

...First, the council professes its belief that God Himself has made known to mankind the way in which men are to serve Him, and thus be saved in Christ and come to blessedness. We believe that this one true religion subsists in the Catholic and Apostolic Church, to which the Lord Jesus committed the duty of spreading it abroad among all men. Thus He spoke to the Apostles: "Go, therefore, and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things whatsoever I have enjoined upon you" (Matt. 28: 19-20). On their part, all men are bound to seek the truth, especially in what concerns God and His Church, and to embrace the truth they come to know, and to hold fast to it.

This Vatican Council likewise professes its belief that it is upon the human conscience that these obligations fall and exert their binding force. The truth cannot impose itself except by virtue of its own truth, as it makes its entrance into the mind at once quietly and with power.

Religious freedom, in turn, which men demand as necessary to fulfill their duty to worship God, has to do with immunity from coercion in civil society. Therefore it leaves untouched traditional Catholic doctrine on the moral duty of men and societies toward the true religion and toward the one Church of Christ...

For Paul VI on the teaching authority of the Council, see here.

...But one thing must be noted here, namely, that the teaching authority of the Church, even though not wishing to issue extraordinary dogmatic pronouncements, has made thoroughly known its authoritative teaching on a number of questions which today weigh upon man's conscience and activity, descending, so to speak, into a dialogue with him, but ever preserving its own authority and force; it has spoken with the accommodating friendly voice of pastoral charity; its desire has been to be heard and understood by everyone; it has not merely concentrated on intellectual understanding but has also sought to express itself in simple, up-to-date, conversational style, derived from actual experience and a cordial approach which make it more vital, attractive and persuasive; it has spoken to modern man as he is...

A majority of the world's bishops participated in the council, and it was convoked by Pope John XXIII, with all of its teaching documents promulgated as authoritative by Pope Paul VI.  It was an ecumenical council.  Ecumenical councils are authoritative. Whether or not we style it "dogmatic" or "pastoral," it was an ecumenical council.  The authority of the Church to teach is laid out in Vatican I:

...We are bound by divine and Catholic faith to believe all those things which are contained in the word of God, whether it be Scripture or Tradition, and are proposed by the Church to be believed as divinely revealed, not only through solemn judgment but also through the ordinary and universal teaching office...— Dogmatic Constitution on the Catholic Faith, ch. 3

If that is an infallible teaching, then when Paul VI said the Council was teaching authoritatively, he would seem to mean that the conciliar texts contain teaching that is "proposed by the Church to be believed as divinely revealed, not only through solemn judgment but also through the ordinary and universal teaching office."

For more on the way in which the Council should be read, see here.  Does this free humans from the obligation to seek the truth in matters religious?  No.  All humans have an abiding obligation to pursue the truth and seek to know and do that which is good, as Pope Benedict says here, and merely following what one believes to be right is not a sufficient justification for doing evil. Excerpts:

...I first became aware of the question with all its urgency in the beginning of my academic teaching. In the course of a dispute, a senior colleague, who was keenly aware of the plight to being Christian in our times, expressed the opinion that one should actually be grateful to God that He allows there to be so many unbelievers in good conscience. For if their eyes were opened and they became believers, they would not be capable, in this world of ours, of bearing the burden of faith with all its moral obligations. But as it is, since they can go another way in good conscience, they can reach salvation...

What I was only dimly aware of in this conversation became glaringly clear a little later in a dispute among colleagues about the justifying power of the erroneous conscience. Objecting to this thesis, someone countered that if this were so then the Nazi SS would be justified and we should seek them in heaven since they carried out all their atrocities with fanatic conviction and complete certainty of conscience. Another responded with utmost assurance that of course this was indeed the case. There is no doubting the fact that Hitler and his accomplices who were deeply convinced of their cause, could not have acted otherwise. Therefore, the objective terribleness of their deeds notwithstanding, they acted morally, subjectively speaking. Since they followed their albeit mistaken consciences, one would have to recognize their conduct as moral and, as a result, should not doubt their eternal salvation.

Since that conversation, I knew with complete certainty that something was wrong with the theory of justifying power of the subjective conscience, that, in other words, a concept of conscience which leads to such conclusions must be false. For, subjective conviction and the lack of doubts and scruples which follow therefrom do not justify man.

Some thirty years later, in the terse words of the psychologist, Albert Gorres, I found summarized the perceptions I was trying to articulate. The elaboration of these insights forms the heart of this address. Gorres shows that the feeling of guilt, the capacity to recognize guilt, belongs essentially to the spiritual make-up of man. This feeling of guilt disturbs the false calm of conscience and could be called conscience's complaint against my self- satisfied existence. It is as necessary for man as the physical pain which signifies disturbances of normal bodily functioning. Whoever is no longer capable of perceiving guilt is spiritually ill, a "living corpse, a dramatic character's mask," as Gorres says.

"Monsters, among other brutes, are the ones without guilt feelings. Perhaps Hitler did not have any, or Himmler, or Stalin. Maybe Mafia bosses do not have any guilt feelings either, or maybe their remains are just well hidden in the cellar. Even aborted guilt feelings ... All men need guilt feelings."

By the way, a look into Sacred Scripture should have precluded such diagnoses and such a theory of justification by the errant conscience. In Psalm 19:12-13, we find the ever worth pondering passage: "But who can discern his errors? Clear thou me from my unknown faults."

That is not Old Testament objectivism, but profoundest human wisdom. No longer seeing one's guilt, the falling silent of conscience in so many areas, is an even more dangerous sickness of the soul than the guilt which one still recognizes as such. He who no longer notices that killing is a sin has fallen farther than the one who still recognizes the shamefulness of his actions, because the former is further removed form the truth and conversion.

Not without reason does the self-righteous man in the encounter with Jesus appear as the one who is really lost. If the tax collector with all his undisputed sins stands more justified before God than the Pharisee with all his undeniably good works (Lk 18:9-14), this is not because the sins of the tax collector were not sins or the good deeds of the Pharisee not good deeds. Nor does it mean that the good that man does is not good before God, or the evil not evil or at least not particularly important.

The reason for this paradoxical judgment of God is shown precisely from our question. The Pharisee no longer knows that he too has guilt. He has a completely clear conscience. But this silence of conscience makes him impenetrable to God and men, while the cry of conscience which plagues the tax collector makes him capable of truth and love. Jesus can move sinners. Not hiding behind the screen of their erroneous consciences, they have not become unreachable for the change which God expects of them, and of us. He is ineffective with the "righteous," because they are not aware of any need for forgiveness and conversion. Their consciences no longer accuse them but justify them...

All that said--humans have freedom of conscience in relation to the state, to the "social and civil" authorities. However, we does not have the freedom of the relativist, able to decide what is good and evil for ourselves--we may only seek to discern what is good or evil. We do not set the standards. They are written into our very natures.  So we must pursue the truth as best we can, as best God enables us to, in order to be saved.  As Pope John Paul II said in Veritatis Splendor:

The splendour of truth shines forth in all the works of the Creator and, in a special way, in man, created in the image and likeness of God (cf. Gen 1:26). Truth enlightens man's intelligence and shapes his freedom, leading him to know and love the Lord. Hence the Psalmist prays: "Let the light of your face shine on us, O Lord" (Ps 4:6)...

Does this mean that people outside the visible bounds of the Church cannot be saved?  According to the Holy Office under Pius XII, no--see here and here. In God's divine mercy, people outside the visible bounds of the Catholic Church can be saved.  Error has no rights, but people do.

So, in submission to the teaching authority of the Catholic Church, I can say: We are rightly free citizens in free societies, with religious freedom and freedom of conscience, rights and freedoms that no government may take away.  As a US citizen, I can say that such religious liberty is mine by God-given right, by the Bill of Rights, and by the intention of the Founders.