Daniel Dennet is a philosopher who is best known for applying evolutionary ideas to philosophical problems such as free will and consciousness. In this book he turns his attention to religious faith. His main idea is that religion is so persistent and so important that it is about time it was properly studied by science. He tries to allay people's fears that this would destroy faith or 'Break the Spell' (in doing so, he shows he has faith in the robustness of religious faith) and also gives some indications of how scientific theories of religion could be constructed and what questions they should answer.
I think this is one of the more accessible of Dennet's books; it doesn't contain as much technical philosopy as Consciousness Explained or Freedom Evolves. I could easily imagine Church of England vicars and bishops reading it (and agreeing with a lot of what it says).
Like all Dennet's books, it is full of memorable phrases and ideas. First, cephalopods as honorary vertebrates:
In the United Kingdom, the law regarding cruelty to animals draws an important moral line at whether the animal is a vertebrate. ... It's a pretty good place to draw the line, but laws can be amended, and this one was. Cephalopods -- octopus, squid, cuttlefish -- were recently made honorary vertebrates, in effect, because they, unlike their close mollusc cousins the clams and oysters, have such strikingly sophisticated nervous systems. ...
Next, the idea of the dilution of responsibility:
Do you ever ask yourself: What if I'm wrong? Of course there is a large crowd of others around you who share your conviction, and this distributes -- and, alas, dilutes -- responsibility, ...
On the arbitrariness of the effects of sexual selection:
And if an influential sample of our female ancestors had happened, for no good reason, to have a taste for males who jumped up and down in the rain, we guys would now find ourselves unable to sit still whenever it rained.
On the creation of religions:
Two or three new religions come into existence every day, ...
On accepting obviously inadequate explanations:
... a disorder often encountered in the humanities and social sciences: premature curiosity satisfaction.
On the importance of written texts to the survival of religions:
A text inked on papyrus or parchment is like the hard spore of a plant that may lie undamaged in the sand for centuries before finding itself in suitable conditions to shed its armour and sprout.
On the immorality of unquestioning faith:
... those who have an unquestioning faith in the correctness of the moral teachings of their religion are a problem: if they themselves haven't conscientiously considered, on their own, whether their pastors or priests or rabis or imams are worthy of this delegated authority over their own lives, then they are in fact taking a personally immoral stand.