Some Christians may hold their noses at the thought of Enlightenment philosophy, believing it to be an exclusively anti-Christian movement. But what we call the Enlightenment included recognizably Christian thinkers in addition to non-Christian ones. To make things even more complicated, philosophers in the Enlightenment were influenced in interesting ways by their more theologically minded contemporaries, regardless of their religious commitments. This lecture explores the philosophy of John Locke (1632–1704) against the theological background of a contemporary, the Reformed scholastic Francis Turretin (1623–1687). Seeing the connections between theology and philosophy in the seventeenth century will help us better understand the Enlightenment — and our world today.