His idea is that the different types of rituals appeal to different fundamental aspects of memory:
"The reason why there are only two types of religion is that there are only two basic systems of memory that matter," he argues. The first is semantic memory, which deals with things we are conscious of remembering and stores what we have learned about the world. Then there is episodic memory, which hangs onto memorable events from our own lives. Whitehouse argues that to persist and spread, a religion must elicit the help of rituals that reinforce memories in both these systems.
So, religions that have little in the way of systematic theology, and instead depend on intense personal experiences, often also feature intense rituals that are stored in episodic memory.
Complex religions that require adherents to memorize shared stories (often counter-intuitive ones) instead feature frequent, low-intensity rituals designed to trigger semantic memories.
It's a nice idea. It's also one that provides an alternative to the more common idea that rituals are 'costly signals' - i.e. by participating, you show that you are sufficiently committed to the group to spend time doing apparently pointless tasks.
But is it true? A good theory makes predictions that you wouldn't otherwise expect. Unfortunately, I don't think the predictions made by Whitehouse's theory fit the bill:
One advantage is that it makes testable predictions. For example, religious rituals are unlikely to be both low frequency and low arousal - because such rituals would not be easily remembered - or high frequency, high arousal - because most people will not willingly undergo too much torment even in the name of religion. It also predicts that doctrinal religions will tend not to have low-frequency, high-arousal rituals because they undermine orthodoxy, and imagistic religions will tend not to have high-frequency, low-arousal rituals because these undermine exclusivity.
To me, it is not surprising that high-arousal rituals are also low-frequency. You could not do penis-cutting every day.
It seems to me that the intensity of frequency of religious rituals are more likely driven by the nature of the society, rather than the type of religion. These imagistic religions occur in small-scale, tribal societies.
What's more, there are plenty of examples of low-frequency, intense rituals within doctrinal religions. Pilgrimages, for example. Not to mention things like Shia self-flagellation and Christian sacramental penance. Of course, Whitehouse is an expert anthropologist so no doubt is aware of these. His argument is that the bulk of religions fit these 'ideals'.
But one interesting deviation is modern Christianity. In the UK at least, many Christians go to church once a year at Christmas time - the very model of a 'low frequency, low arousal' ritual!