In this paper I examine William Alston's work on the epistemology of religious belief, focusing on the threat to the epistemic status of Christian belief presented by awareness of religious diversity. I argue that Alston appears to misunderstand the epistemic significance of the ‘practical rationality’ of the Christian mystical practice. I suggest that this error is due to a more fundamental misunderstanding, regarding the significance of practical rationality, in Alston's ‘doxastic practice’ approach to epistemology; an error that leads to arbitrariness among the class of rational doxastic practices. I suggest how one might remedy this weakness, with an additional, epistemic, criterion that rational doxastic practices must satisfy.