John Locke wrote four letters concerning toleration in his lifetime. The most famous of these was the Epistola de Tolerantia (Letter Concerning Toleration), written in 1685; Locke wrote the letter to his friend Philip von Limborch. This letter is the most general of all four letters concerning toleration. Locke’s understanding of toleration can be summed up as follows: every person ought to be permitted to worship as their conscience dictates; the government may not make laws requiring religious attendance at a state specified Church; but that does not mean the government may not promote religion through persuasion as every other citizen is permitted.
There are found topics concerning toleration discussed throughout the first letter. The first is toleration as the characteristic of the True Church. Secondly, Locke discusses the role of the government in religion. He then discusses the Church, defining it and describing the powers granted unto it. Locke then discusses the bounds placed on religion by toleration and then the bounds placed on the society by toleration
“That I esteem that Toleration to be the chief Characteristical Mark of the True Church.”  Locke asserts that the toleration is above all the duty of a Christian as given to humanity by Christ. Christians must first concern themselves with their own salvation before they can assume to tell others about salvation. In order for someone to be saved, they must sincerely believe in Christ as their savior. This notion dictates that forcing someone to worship in a manner contrary to their own consciousness would in fact futile to the desired end. Locke asserts, “The Toleration of those that differ from others in Matters of Religion, is so agreeable to the Gospel of Jesus Christ, and to the genuine Reason of Mankind, that it seems monstrous for Men to be so blind, as not to perceive the Necessity and Advantage of it, in so clear a Light.” A Christian must not punish those who do not believe in the same faith.
As having asserted that toleration is the chief characteristic of the True Church, Locke demonstrates the boundaries of Civil Government from that of Religion. Locke begins his discussion of Civil Government and Religion by saying, “The Commonwealth seems to me to be a Society of Men constituted only for the procuring, preserving, and advancing of their own Civil Interests.”  He labels the “Civil Interests” to be, “Life, Liberty, Health, and Idolency of Body; and the Possession of outward things, such as Money, Lands, Houses, Furniture and the like.” The duty of the sovereign is procure these goods and other goods necessary for this life. Thus it is inherently not the duty of the magistrate to legislate religion for the salvation of the soul. The authority of salvation of souls is not granted to the magistrate by God, nor can it be granted to the magistrate by the People. Locke explains:
Nor can any such Power be vested in the Magistrate by the consent of the People; because no man can be so far abandon the care of his own Salvation, as blindly to leave it to the choice of any other, whether Prince or Subject, to prescribe to him what Faith or Worship he shall embrace. 
The power of salvation must lie in the hands of the individual citizen for his or her own salvation, because as Locke describes, “All the Life and Power of true Religion consists in the inward and full perswasion of the mind; and Faith is not Faith without believing.”
Secondly, the magistrate creates laws that have punishments when the law is not followed, thus to create laws dictating religion would place punishment on those who do not follow the law; further it would coerce individuals to follow the state religion against their own consciousness.  While the magistrate is not permitted to create laws concerning religion, Locke does say:
It may indeed be alledged, that the Magistrate may make use of Arguments, and thereby draw the Heterodox into the way of Truth, and procure their Salvation. I grant it; but this is common to him with other Men. In teaching, instructing, and redressing the Erroneous by Reason, he may certainly do what becomes any good man to do. Magistracy does not oblige him to put off either Humanity or Christianity. But it is one thing to perswade, another to command; one thing to press with Arguments, another with Penalties. This Civil Power alone has a right to do; to the other Good-will is Authority enough. Every Man has Commission to admonish, exhort, convince another of Error and by reasoning to draw him into Truth; but to give Laws, receive Obedience, and compel with the Sword, belongs to none by the Magistrate. 
This is the sum of the authority of the magistrate in matters of religion, which he receives by virtue of his humanity.
In the third place, Locke argues that the magistrate cannot involve himself in religion because there is only one way to Heaven. Since no one knows what the true religion is, forcing someone to obey a state religion could mean the damnation of that person’s soul. 
Moving on, Locke defines a church as:
A Church then I take to be a voluntary Society of Men, joining themselves together of their own accord, in order to the publick worshipping of God, in such a manner as they judge acceptable to him, and effectual to the Salvation of their Souls.
A person must come to religion on their own accord; no one is born a member of a church as a result. re can be no state mandated religion or Church as a result. The church, as a voluntary society, must be permitted to create laws that all members consent to in order to survive. These laws consist of the following:
- “Place and time of meeting…”
- “Rules for admitting and excluding Members…”
- Distinction of Officers and putting things into a regular Course, and such like…”
Like the Civil Society, a Church cannot punish a member save removing them from the Church. Churches must have a ruler established and consented to by the members of the Church. And as in Civil Society, Locke argues that no man can be forced to belong to a Church without consenting to his representatives. 
This thus ends the argument concerning what the Civil Society and Church are permitted to do. Locke then discusses toleration in regards to both Civil Society and Church. The Church is bound by toleration, first, by removing any person from the communion of the Church after continuing to disobey the Laws of the Society.  is it that a Church may remove a member? Locke responds, “For these being the Condition of Communion, and the Bound of the Society, if the Breach of them were permitted without any Animadversion, the Society would immediately be thereby dissolved.”
Private Citizens are bound by Toleration as well, Locke states, “nor ought any private Persons, at any time, to use Force; unless it be in self-defence against unjust Violence. Excommunication neither does, nor can, deprive the excommunicated Person of any of those Civil Gods that he formerly possessed.”the same manner the private citizens is not permitted use prejudice against any person based on his or her religious beliefs. 
When the Magistrate joins himself with a specific church and religion he does not grant any new rights to the church or religion that they did not already possess; in the same light the church or religion does not grant any new authority the Magistrate.  right of a society to remove members that disobey the laws that were consented to cannot be denied according to Locke; however the church society does not have a right to acquire any new rights over those that are not members.Churches are bound to toleration in these manners, that they may create laws and a ruling body based on the consent of their members, also that they may remove those members but may not infringe on their life, liberty or property, and finally that they are not permitted to exercise any authority over persons not members of the church society.
Locke finishes his letter with a discussion of how the Civil Society is bound to toleration.  Locke has already established that the magistrate does not have the authority to create laws requiring individuals to attend a specific church, worship in a specific manner and believe in a specific deity. He reiterates this by saying, “Not a Magisterial Care, I mean, which consists in prescribing by Laws, and compelling by Punishments. But a charitable Care, which consists in teaching, admonishing, and persuading, cannot be denied unto any man.” Laws can be created for the protection of goods and health of the members of the society. He sets out to discredit the belief that the magistrate can dictate the religious beliefs of the society through laws. The question is finally asked by Locke, “If the Religion of any Church become therefore true and saving, because the Head of that Sect, the Prelates and Priests, and those of Tribe, do all of them, with all their might, extol and praise it; what Religion can ever be accounted erroneous, false and destructive?” Another problem with the magistrates dictating religion is that when one magistrate dies and another takes his place the beliefs of the religion might be changed. He points to the reformation monarchs of England and demonstrates how the religious beliefs of the national church changed as each monarch ascended to the throne. Thus Locke asserts:
I may grow rich by an Art that I take not delight in; I may be cured of some Disease by Remedy that I have not Faith in; but I cannot be saved by a Religion that I distrust, and by a Worship I abhor. It is in vain for an Unbeliever to take up the outward shew of another mans Profession. Faith only, and inward Sincerity, are the things that procure acceptance with God.
From this Locke discusses toleration on two levels, the outward worship of the religious society and the inward worship. In regards to the outward worship, Locke believes that the magistrate has no authority in prescribing the manner of worship through law. This power is held away from the magistrate because the church is a free society, permitted to create its own rules concerning the outward worship of its members. Law may only be created with the ends of the public good in mind, not with the salvation of individual souls, which is the responsibility of the individual person. Locke does permit the magistrate’s interference into religion when the ceremonies used by the church endanger the life, liberty or property of the members.  The magistrate has authority as well, if it prove to be beneficial to the society, to order aspects of the outward worship be practiced by the society; Locke uses the example of infant baptism, that if it proves to protect against disease then the magistrate has authority to order all infants to be washed. Locke once again proposes that, “Whatsoever is lawful in the Commonwealth, cannot be prohibited by the Magistrate in the Church.” For example, if it is legal for a man to slaughter a chicken in his home then he must be allowed to slaughter a chicken for sacrifice in church. Laws that are passed to prohibit a religious sect from performing an outward symbol of worship must be general and political. That is to say that the law must apply to all citizens for the specific purpose of the public good.
After discussing the manner of outward worship, Locke moves to the inward worship of religions. He separates inward worship into two categories: the speculative opinions and practical articles of faith. As to the speculative opinions, the magistrate is not permitted to forbid the preaching or profession of such opinions. For example, a Roman Catholic should be allowed to believe the bread and wine becomes the body and blood of Jesus Christ; the Jew should be allowed to believe the New Testament to be false. 
As for the practical Locke begins by saying:
A Good Life, in which consists not the least part of Religion and true Piety, concerns also the Civil Government: and in it lies the safety both of Mens Souls, and of the Commonwealth. Moral Actions belong therefore to the Jurisdiction of both the outward and inward Court; both of the Civil and Domestick Governor; I mean, both of the Magistrate and Conscience.
The religious beliefs of the individual must not infringe on the rights of another man. The beliefs of a religion cannot be contrary to the public good as dictated by the law. All persons are obligated to follow the law when it is for the public good; but one may also go against the law if it is not for the public good. The commonwealth’s authority extends only to those things of this life, not of the afterlife; thus they may not legislate laws that protect the interests of persons in this life.  A religion cannot profess that its members assume the mantle of responsibility that is already granted to the commonwealth. That is to say, the responsibility of the religion is to help in the salvation of the souls of its members; the religion may not profess to have any control over the public good.
At this point Locke engages a discussion of instances when the magistrate is no longer bound to tolerate a specific religious sect:
No Opinions contrary to human Society, or to those moral Rules which are necessary to the preservation of Civil Society, are to be tolerated by the Magistrate. But of these indeed Examples in any Church are rare. For no Sect can easily arrive to such a degree of madness, as that it should think fit to teach, for Doctrines of Religion, such things as manifestly undermine the Foundations of Society, and are therefore condemned by the Judgment of all Mankind: because their own Interest, Peace, Reputation, every Thing, would be thereby endangered.
There is an inherent obligation of religion to teach its members to obey the laws of the commonwealth. If the religion teaches something contrary to the public good, the magistrate has an obligation not to tolerate it. The religion may also not profess authority to relieve members of allegiance to the prince of the commonwealth. Locke says, “That Church can have no right to be tolerated by the Magistrate, which is constituted upon such a bottom, that all those who enter into it, do thereby, ipso facto, deliver themselves up to the Protection and Service of another Prince.” Finally Locke lists another set of person that should not to be tolerated by the magistrate:
Those are not at all to be tolerated who deny the Being of a God. Promises, Covenants, and Oaths, which are the Bonds of Humane Society, can have no hold upon an Atheist. The taking away of God, tho but even in thought, dissolves all. Besides also, those that by their Atheism undermine and destroy all Religion, can have no pretence of Religion whereupon to challenge the Privilege of a Toleration. As for other Practical Opinions, tho not absolutely free from all Error, if they do not tend to establish Domination over others, or Civil Impunity to the Church in which they are taught, there can be no Reason why they should be tolerated. 
In the end, Locke sums up his beliefs of who is to be tolerated and who is not to be tolerated:
Those that are Seditious, Murderers, Thieves, Robbers, Adulterers, Slanders, etc. of whatsoever Church, whether National or not, ought to be punished and suppressed. But those whose Doctrine is peaceable, and whose Manners are pure and blameless, ought to be upon equal Terms with their Fellow-Subjects.
Locke’s understanding of toleration extends to both the commonwealth and the church. Religions must obey laws established for the public good, while in the same light the commonwealth may not pass laws specifically prohibiting a certain religion from doing something allowed to other citizens. Religions have the same rights granted to them that any other private association would have. Persons are required to believe in some sort of deity, and those that act contrary to the public good are not to be tolerated at all. For Locke the idea of toleration is at times simple but can become very complex at the same time. Religion has no right to involve itself in the public affairs, while the commonwealth may involve itself in private affairs when those affairs act contrary to the public good.
Introduction of Letter Concerning Toleration by John H. Tully
LCT. Pg 23. in Tully
LCT. Pg. 23 in Tully
“It would indeed be very hard for one that appears careless about his own Salvation, to persuade me that he were extreamly concern’d for mine.”- LCT. Pg. 23 in Tully
Desired end of Christian salvation is to be saved, however one cannot be saved if they do not sincerely believe in Christ.
LCT. Pg. 25 in Tully
“I esteem it above all things necessary to distinguish exactly the Business of Civil Government from that of Religion, and to settle the just Bounds that lie between the one and the other.”- LCT, pg. 26 in Tully.
LCT. Pg. 26 in Tully
LCT. Pg. 26 in Tully
“Now that the whole Jurisdiction of the Magistrate reaches only to these Civil Concernments; and that all Civil Power, Right and Dominion, is bounded and confined to the only care of promoting these things; and that it neither can nor ought in any manner to be extended to the Salvation of Souls..” LCT, pg. 26 in Tully.
LCT pg. 26 in Tully
LCT. Pg 26 in Tully
“The care of Souls cannot belong to the Civil Magistrate, because his Power consists only in outward force; but true and saving Religion consists in the inward perswasion of the Mind, without which nothing can be acceptable to God.”- LCT Pg. 27 in Tully
LCT. Pg 27 in Tully; cross reference with page 35 “In the last place..”
“For there being but one Truth, one way to Heaven; what Hopes is there that more Men would bed led into it, if they had no Rule but the Religion of the Court, and were put under a necessity to quite the Light of their own Consciences, and blindly to resign up themselves to the Will of their Governors…” LCT, Pg 27
LCT, pg 28 in Tully
“No Man by nature is bound unto any particular Church or Sect, but ever one joins himself voluntarily to that Society to which he believes he has found that Profession and Worship which is truly acceptable to God.”- LCT, pg. 28 in Tully
LCT, pg. 28 in Tully
LCT pg. 30 in Tully
LCT, Pg. 29 in Tully
“That no Church is bound by the Duty of Toleration to retain any such Person in her Bosom, as, after Admonition, continues obstinately to offend against the Laws of the Society.”- LCT, Pg. 30 in Tully
LCT Pg. 30 in Tully
LCT Pg. 31 in Tully
“No private Person has any Right, in any manner, to prejudice another Person in his Civil Enjoyments, because he is of another Church or Religion”- LCT Pg. 31 in Tully
“For the Civil Government can give no new Right to the Church, nor the Church to the Civil Government.”- LCT Pg. 31 in Tully
“This is the fundamental and immutable Right of a spontaneous Society, that it has power to remove any of its Members who transgress the Rules of its Institution: But it cannot, by the accession of any new Members, acquire any Right of Jurisdiction over those that are not joined with it.”- LCT pg. 31 in Tully
“Let us now consider what is the Magistrate’s Duty in the Business of Toleration: which certainly is very considerable.”- LCT pg. 35 in Tully.
LCT pg. 35 in Tully
“Laws provide, as much as is possible, that the Goods and Health of Subjects be not injured by the Fraud or Violence of others…”-LCT pg. 35 in Tully.
LCT pg 37 in Tully
“that the Magistrate has no Power to enforce by Law, either in his own Church, or much less in another, the use of any Rites or Ceremonies whatsoever in the Worship of God. And this, not only because these Churches are free Societies, but because whatsoever is practiced in the Worship of God, is only so far justifiable as it is believed by those that practice it to be acceptable unto him.”- LCT pg. 39 in Tully
“The only business of the Church is the Salvation of Souls: and it no ways concerns the Common-wealth, or any Member of it, that this, or the other Ceremony be there made use of. Neither the Use, nor the Omission of any Ceremoney in those Religious Assemblies, does either advantage or prejudice the Life, Liberty or Estate of any man.”- LCT pg. 39 in Tully
“Let it be granted also, that if the Magistrate understand such washing to be profitable to curing or preventing any Disease that Children are subject unto, and esteem the matter weighty enough to be taken care of by a Law, in that case he may order it to be done.”- LCT pg. 40 in Tully
LCT pg. 42 in Tully
“The Magistrate ought not to forbid the Preaching and Profession of any Speculative Opinions in any Church, because they have no manner of relation to the Civil Rights of the Subjects. If a Roman Catholick believe that to be really the Body of Christ, which another man calls Bread, he does no injury thereby to his Neighbour. If a Jew do not believe the New Testament to be the Word of God, he does not thereby alter any thing in mens Civil Rights.”- LCT pg. 46 in Tully
“For the Political Society is instituted for no other end but only to secure every mans Possession of the things of this life.”- LCT pg. 48 in Tully.
LCT pg. 49 in Tully
LCT pg. 50 in Tully
LCT pg. 51 in Tully
For modern example of this principle see Church of Lukumi Babalu Ave., Inc. v. Hileah. 113 S. Ct. 2217 (1993). Supreme Court ruled a law passed by the Hileah to be unconstitutional because it barred the Lukumi from practicing sacrifice despite not outlawing slaughtering in general.
Locke was aware of the fact that the Roman Catholic Church was already in the process of changing her views on this subject.