This book puts forward a model for thinking about the way religious ideas are transmitted. Whitehouse's theory tries to explain how religions are propagated in the first place, and what their enduring appeal is – particularly, what motivates people to reproduce religious knowledge? What makes spiritual experiences memorable, or ingrained?
Whitehouse separates religion into two modes: imagistic and doctrinal. I think his descriptions of each ring true for what we observe in various religious experiences. Imagistic experiences are immediate, localised, often traumatic, and thus highly memorable. Trauma becomes a part of you, but it's difficult to transfer because it's something entirely personal. On the other hand, doctrinal modes of transfer are characterised by heavy repetition, orthodoxy, anonymity, and are centralised.
It's a neat way of thinking about transmission, but quite difficult to test. There does seem to be some support in the area of neuroscience – different types of religious experiences do engage the brain in predictable ways. It's just very difficult to work out how relevant that data actually is; the brain is highly connected, and activity in one area may not always indicate straightforwardly how somebody feels. I also suspect that what he may be dichotomising what is essentially a continuum, as I feel both modes inform and support each other in many religions.
In any case, I think this book is important because it locates religiosity in the underlying mechanisms linked to emotions, feelings and perception. It makes it more difficult to envisage belief as something backward or unprecedented, and instead just a side-effect of structures that are deeply part of all humans.