The goal of this paper is to explicate the theological and epistemological elements of John Locke's moral philosophy as presented in the ‘Essay Concerning Human Understanding’ and ‘The Reasonableness of Christianity’. Many detractors hold that Locke's moral philosophy is internally inconsistent due to his seeming commitment to both the intellectualist position that divinely instituted morality admits of pure rational demonstration and the competing voluntarist claim that we must rely for our moral knowledge upon divine revelation. In this paper I argue (...) that Locke is guilty of no such contradiction. In doing so, I attempt to accommodate Locke's position in the ‘Essay’ that moral principles are demonstrable a priori with his views on the sanctity of Christian revelation. I then consider Locke's conception of moral ideas as a species of mixed modes, or arbitrarily constructed complex ideas, and attempt to navigate the mechanism whereby human understanding can recognize these ideas as conforming to, or straying from, divinely appointed natural law. I conclude that despite Locke's failure to actually provide a full-fledged moral theory, he lays a rationally coherent groundwork for the fulfilment of such a project that accommodates a-priori rational reflection and divine revelation as complementary paths to moral understanding. (shrink)