Although toleration is today not infrequently preached by Christian authorities, it is important to recall that the tradition of Christianity is one of intolerance. Unlike most contemporary religions, Christianity was, from Pauline times, an exclusivistic religion, forbidding its votaries to worship other gods or engage in alien practices. It was also a universalistic religion, proclaiming that it was the only true religion for all mankind. Whereas Judaism was also exclusivist, it was not universalist—it was not a religious choice normally available to those who were not ethnic Jews. Christianity, in contrast, taught that it was the only valid religion for anyone at all. It was a voluntaristic religion which men were free to choose, and should choose. Thus, Christianity was also a proselytizing religion, seeking to persuade people that all other religions were evil, and condemning them as such.
For centuries, the Christian church made its main mission the conversion of the heathen, among whom it included those of all other faiths. While the heathen were to be converted, those who were acquainted with “the true faith” but had, in some particular or another, come to challenge church teaching were to be not only excommunicated from the church but also exterminated by death (the authoritative demand of St. Thomas Aquinas).
Christian intolerance towards all other faiths was mitigated only at the Reformation, and then only gradually. The early manifestations of toleration in central Europe were initially applicable only to princes, whose subjects were required to adopt the faith, Catholic or Lutheran, of their ruler on the principle adopted at the Peace of Augsburg in 1555, of cuius regio, eius religio [in a prince’s country, a prince’s religion]. In the various territories influenced by the Calvinist Reformed Church, toleration was sometimes subsequently extended to Calvinists, but the sects of the so-called “radical” Reformation—Anabaptists and Hutterites—and later, the Socinians and Unitarians continued to be persecuted, whilst atheists were not to be tolerated at all according to theories of toleration advanced even by enlightened philosophers such as John Locke.
The best guarantee against social divisiveness in such a religiously pluralist society was not to be found in an attempt to impose religious conformity but in the establishment of religious toleration as a principle transcending the doctrines and beliefs of any one religion.
Eventually, the principles espoused by the Reformation of an “open Bible” and “the priesthood of all believers” led to the steady attrition of the dispositions of intolerance enshrined in traditional Christianity. Dissenting groups acquired limited rights to worship in their own preferred way, in England most conspicuously under the legislation of William and Mary in 1689. Restrictions remained and were only gradually relaxed and eventually abated in the subsequent two hundred years. Gradually the governing classes of Europe came to abandon the theory that social cohesion largely depended on the maintenance of religious conformity. The lesson was more pointedly realized in the United States, where a religiously diverse population (among whom were many refugees from religious persecution in Europe) had to be accommodated. The best guarantee against social divisiveness in such a religiously pluralist society was not to be found in an attempt to impose religious conformity but in the establishment of religious toleration as a principle transcending the doctrines and beliefs of any one religion. In contrast to the old European assumptions of the need for religious coercion, in the United States it was recognized that a principle of toleration was indispensable for the social cohesion of an already religiously diversified population. Thus it was, that in the American context, toleration and religious freedom were invoked as principles superordinate to any particular religious system. The very creation of a secular state, in which the governing authorities were not to establish religion nor to show partiality for any one religion above another, became the first guarantee of religious rights.