Understanding C.S. Lewis's vocation is essential for reading his works well, as is knowing how he came to it: his long and winding philosophical journey and reoccurring experiences of 'Joy.' Lewis discounted 'proofs' in philosophical theology but offered key arguments in support of theism per se, and Christianity in particular. His account of "mere Christianity" shows the centrality of self-determination, an emphasis on Christ's human nature, and a relativizing of atonement theories. Finally, Lewis's understanding of faith, his attempts to make sense of petitionary and imprecatory prayers, and his emphasis on theosis/deification, are considered.