Jo - I think you will be surprised to find out that many of your co-religionists are, actually, in pretty much the same boat and don't 'really' believe 90% of the stuff they parrot (eg who really believes Exodus:12:29-30 nowadays?)

What people do have is a general feeling that there is a God(s) (seems to be almost hardwired in Human brains, and hard to overcome), and a liking for the companionship and structure that a religion brings.

Belief in Belief, as Dennett calls it in 'Breaking the Spell', which is good book to read..