A Possible Answer

Meme theory is the notion that cognitive items--ideas, phrases,etc.--can be subject to evolutionary pressures. So let's say we have some dubious religious idea. What happens if we add to it provisos that it is absolute truth, that you are deep trouble if you don't truly believe it, and that it is known to be true by faith and is thus impervious to logical disproof? A dubious idea with these provisos would be more likely to be reproduced--maintained in your own mind and passed on to others--than a dubious idea without them. And then what would be the effect of making the idea not only dubious, but to a degree nonsensical or unintelligible? An idea you want to reproduce, remember, pass on to others, that is also not really intelligible, is more likely to be passed on verbatim. More likely to be passed on without mutation because paraphrasing something you don't really understand is difficult. Thus we stand up together reciting creeds.