John Locke formulated a classic reasoning for religious tolerance which can be seen in his Letters Concerning Toleration (1689–1692).
Three arguments were central to his reasoning: judges, state or human beings are not capable of evaluating the truth-claims of competing religious standpoints; enforcing a single religion would have an adverse effect as faith cannot be compelled by violence; and coercing religious uniformity would lead to more social disorder than allowing diversity.
Furthermore, he believed that those holding political power were no better at discovering the true religion than anyone else and so they should not attempt to enforce their views on others.
Locke did place a limit to tolerance stating that any religious group which posed a threat to political stability or public safety should not be tolerated. Locke’s writings on tolerance were very progressive for the time. However, he believed that atheists should not be tolerated as lack of faith made them untrustworthy and irresponsible.