It is often assumed that Locke, as an early Enlightenment figure, sought to reduce Christianity to a moral code. His presumed aim was to downplay its supernatural claims, especially the contentious doctrines of sin, judgment and redemption. For this reason Christian conservatives tend to suspect Locke of deism, unitarianism or worse. Liberal interpreters of Locke, on the other hand, approve his attempt to tame the passions of religion by making Christianity more earthly minded—they just don’t believe that he went far enough.

Consider the counsel of Ayaan Hirsi Ali, a former Muslim turned agnostic, to the advocates of liberal Islam. She argues that Islam’s “fixation on the afterlife” has “pernicious” consequences for religion and politics. In her book Heretic: Why Islam Needs a Reformation Now, Hirsi Ali says it’s time for Muslims to learn from the story of Christianity’s transformation into a more tolerant faith. “Only when Islam chooses this life can it finally begin to adapt to the modern world.”

The history of religiously inspired violence gives her argument a certain resonance, at least to secular-minded intellectuals. Whether pious Muslims will welcome it, of course, is another matter. But there’s a problem with this account of the development of religious toleration in the West: It ignores the moral narrative that ultimately helped to defeat the opponents of toleration.

Locke’s contempt for coerced religion did not grow from the soil of skepticism or unbelief. Rather, it was born of the conviction that militant religion threatened the eternal souls of its victims. “Every man has an immortal soul,” he writes in the Letter, “capable of eternal happiness or misery.” Thus it is man’s “highest obligation” to seek God’s favor “because there is nothing in this world that is of any consideration in comparison with eternity.” The argument appears often in Locke’s many writings on toleration, and he deploys it repeatedly in the Letter, like a battering ram to smash the base motives of the advocates of coercion. “A sweet religion, indeed,” he writes, “that obliges men to dissemble, and tell lies both to God, and man, for the salvation of their souls!”

Rather than downplaying the doctrines of divine judgment and salvation, Locke raises the stakes:

Although the magistrate’s opinion in religion be sound, and the way he appoints be truly evangelical, yet, if I be not thoroughly persuaded thereof in my own mind, there will be no safety for me in following it. No way whatsoever that I shall walk in against the dictates of my conscience will ever bring me to the mansions of the blessed. I may grow rich by an art that I take not delight in, I may be cured of some disease by remedies that I have not faith in; but I cannot be saved by a religion that I distrust, and by a worship that I abhor. . . . Faith only, and inward sincerity, are the things that procure acceptance with God.

Here is the voice not of a rationalist who doubted the efficacy of coercing people to believe, but rather a moralist offended by the attempt to do so. For Locke, the ultimate objective of religious worship is the attainment of eternal life. His insight is to use this religious premise to support a political conclusion: that the only state worthy of political loyalty is one that permits every citizen to pursue this spiritual goal on his or her own terms.

Probably every reform movement in Christian history has justified itself with appeals to the example of Jesus. This was true of the sixteenth-century Christian humanists, such as Desiderius Erasmus, whose “philosophy of Christ” exerted a profound influence on Locke’s conceptual approach to toleration. Erasmus, a leading Catholic scholar, made the life and teachings of Jesus the fulcrum for social change. “What else is inculcated by his precepts, his parables, and his practice, but peace and mutual charity?” he wrote. The faithful Christian, Erasmus explained, was the person “who piously reflects on these writings, praying rather than disputing, and seeking to be transformed within rather than armed for battle.”

Locke stands firmly in this humanist tradition. Just as in the Two Treatises, his opening argument in the Letter is not aimed at political authorities or to individuals as political actors. Instead, he addresses the community of Christian believers. They were the custodians of the European political conscience. Their values and beliefs help shape the civic and political culture. It is to religious believers that Locke must first make the moral case for freedom of conscience.

Locke begins by declaring, unequivocally, that toleration is the chief mark of the “true church.” Appeals to theological orthodoxy are meaningless, he insists, without this virtue visible in personal and corporate life. “Let anyone have ever so true a claim to all these things,” he writes, “yet if he be destitute of charity, meekness, and goodwill in general towards all mankind, even to those that are not Christians, he is certainly yet short of being a true Christian himself.”

Though Locke enlists the Bible only sparingly in his Letter, we know from his private journals that during this time he was studying the Bible carefully for principles that he believed supported toleration. A journal entry under the heading “Tolerantia Pro,” dated 1688, a year before the publication of the Letter, lists twenty-one passages from the Hebrew and Christian Bible. Included is a climactic scene from the gospel of Luke, which records the remarkable prayer of Jesus at the cross, asking God to forgive his executioners: “Then Jesus said, ‘Father, forgive them; for they know not what they do.’” The unifying theme of these passages is unambiguous: near the heart of Locke’s Christology is the concept of charity and forgiveness, even toward the most debased and violent of sinners.

Thus in his Letter, Locke interprets the moral life of Jesus as a bracing defense of religious toleration:

If, like the Captain of our salvation, they sincerely desired the good of souls, they would tread in the steps and follow the perfect example of that Prince of Peace, who sent out his soldiers to the subduing of nations, and gathering them into his church, not armed with the sword, or other instruments of force, but prepared with the Gospel of peace, and with the exemplary holiness of their conversation. This was his method.

The phrase “Captain of our salvation,” taken from the Letter of Hebrews in the New Testament, was a popular metaphor among the preachers of Locke’s day. It communicated an image of Christ as one who would not answer violence with violence, but suffered patiently to win salvation for God’s people. Likewise, the expressions “Prince of Peace” and “Gospel of Peace” are scriptural references emphasizing the themes of reconciliation.

Locke’s opening salvo, embedded in biblical idioms, argues that the only means approved by Jesus for spreading his message are those of preaching, dialogue and debate. Such efforts would be characterized by their “exemplary holiness,” in other words, by calm, gracious and rational persuasion. If Jesus did not employ force to win converts, neither could his followers, whether through the institutions of church or state. Cynics, heretics, pagans—they must be allowed to go their own way. Here is the theological basis for a pluralistic society.

THE CORE concepts underlying Locke’s thought—the universal gift of reason, the belief in eternal life and the moral example of Jesus—now combine toward a political end. Together they support the political theory for which Locke is rightly famous: the doctrine of consent, the idea that all legitimate political authority is rooted in the consent of the governed.

The revolutions in the Arab world that began in 2011, though varied in each country, shared at least one trait: they paid homage to this concept of the social contract. In each case—whether in Tunisia, Libya, Syria or Egypt—they began as a protest against arbitrary or absolute rule. In each case, the revolutionaries believed the contract between ruler and ruled had been violated. The Arab Spring initially bore the marks of a Lockean revolution.

Why have nearly all of these revolutions failed? Why have they devolved into a Hobbesian “perpetual war” of “every man against every man”? The reasons are complex, but among them is a deficit in the political culture of modern Islam: the failure to see the vital bond between religious freedom and democratic self-government. Locke understood their mutual relationship. Though modern scholars mostly ignore the connection, it is clear that Locke’s political principle of consent owed a great debt to its religious counterpart, the consensual nature of faith.

A voluntary faith must be worked out in a voluntary society, i.e., the church of one’s choice. “The hope of salvation, as it was the only cause of his entrance into that communion, so it can be the only reason to stay there,” Locke writes in his Letter. “No member of a religious society can be tied with any other bounds but what proceed from the certain expectation of eternal life.” Here is Locke’s decisive break with the prevailing view of religious identity as being rooted in family, geography or political regimes. Unlike property or wealth, he argues, an individual’s faith cannot be inherited; it must be appropriated through judgment, choice and consent. The same holds true for membership in a community of believers: the church must be understood as a “free and voluntary society.”