Recently, scholars have disputed whether Locke's political theory should be read as the groundwork of secular liberalism or as a Protestant political theology. Focusing on Locke's mature theory of toleration, the article raises a central question: What if these two readings are compatible? That is, what would be the consequences if Locke's political philosophy has theological foundations, but has also given shape to secular liberalism? Examining Locke's theory in the Letter Concerning Toleration (1689), the article argues that this is indeed (...) the case. The liberal model of toleration is a secularization of the theology of Christian liberty and its division of society into a temporal political kingdom and the spiritual kingdom of Christ. Therefore, when liberal toleration travels beyond the boundaries of the Christian West or when western societies become multicultural, it threatens to lose its intelligibility. (shrink)