Christopher Buckley's Varieties of Religious Experience
Not all of these, but many of these have a dense complexity of spirituality mixed with an intellectualism that makes the whole collection dense. This is just to say, it's not a collection that you're going to want to read in one sitting. I've been bouncing between Winston Churchill and Christopher Buckley in my reading and of the two Buckley is definitely the more moving. I've been a fan for year, and I enjoy this collection a lot. I love its scientific and metaphysical, and it definitely stretches the brainpan.