What did John Locke argue in A Letter Concerning Toleration?

In A Letter Concerning Toleration, John Locke argued that religious intolerance stems from a failure to distinguish between the proper domains of religion and government.1

Locke contended that the state’s legitimate purpose is limited to protecting "civil interests"—specifically life, liberty, and property—and that it lacks the authority to coerce individuals in matters of salvation. Because genuine faith requires the "inward and full persuasion of the mind," he argued that state-mandated worship is ineffective and contrary to the nature of a true church, which he defined as a voluntary association.1

While advocating for toleration as a fundamental principle, Locke’s position was not absolute. He excluded atheists and Roman Catholics from his framework, arguing that the former could not be trusted to uphold covenants and that the latter’s allegiance to a foreign power (the pope) threatened civil authority. Ultimately, his work laid the foundation for the modern concept of the separation of church and state.1