In reply to Gordon Stainforth:
I agree that Christianity did not come from nowhere, but was superimposed on - and made use of - a pre-existing, shared cultural background. What mystifies me is that much of that background is shared with Islam, itself a spin-off of Judaism and Christianity in much the same way Christianity arose from Judaism. Again, what makes the two religions, or more precisely the societies shaped by them, differ, so that a region culturally defined by one religion (and I hope we can agree that the society Kant operated in was shaped by Christian cultural and religious tradition) was amenable to enlightenment, while the other, that was initially ahead civilizationally, eventually regressed?
Ockham´s razor would suggest that the difference lies within the religions themselves, but I could happily be convinced otherwise if someone had a good alternative explanation.
Just to make sure, personally I do not believe in the existence of gods, not even as nonpersonal creators, and am convinced that religiosity arises in our brains as an accidental by-product of our evolution: Essentially, the strong selective benefit toward attributing causality (the twig does not snap itself, maybe there is a bear behind the bush, better run right now ...) eventually led to inventing causes for as yet unexplained phenomena (someone must make the clouds release rain...). Also, there may initially have been a selective advantage for groups (contentious, I know) that could enforce social cohesion by invoking a higher authority.
As for the other question, why Europe and not South America, I recommend Jared Diamond´s book "Guns, Germs, and Steel", where he makes a good argument why geography gave budding near eastern civilizations a head start following the end of the last ice age. Why Greece in particular I don´t know, but will definitely have a look at the book you recommended.
CB