What is the main conflict in An Essay Concerning Human Understanding by John Locke?

John Locke's An Essay Concerning Human Understanding is a major work in the history of philosophy and a founding text in the empiricist approach to philosophical investigation. Although ostensibly an investigation into the nature of knowledge and understanding (epistemology) this work ranges farther afield than one might expect. Instead of just being merely a work in epistemology, this is really a reappraisal of many traditional philosophical questions, metaphysical, epistemological, ethical, and religious.