They might.
My model has it as a code for clerics by clerics. If you don't want to actually work for a living, say by tilling the soil or raising the flocks, you have to convince somebody to support you. Tell them that they are unclean (and they're probably pretty stinky anyway, no water, no baths) and they need to perform some act to make them (ritually) clean. A side effect of the cleaning ritual is that you have all these sacrificial (and really valuable in the society in question) carcasses to dispose of. Burn a few of them and show the bodies to make sure that the serfs don't want them back and to have the nasty smell cover the fact that you are cooking the rest of them. Eat in private. Use a powerful imaginary friend for security and voi-la, you've got Levites. It's their gig for a few thousand years.
I find this a pretty plausible scenario.
My model has it as a code for clerics by clerics. If you don't want to actually work for a living, say by tilling the soil or raising the flocks, you have to convince somebody to support you. Tell them that they are unclean (and they're probably pretty stinky anyway, no water, no baths) and they need to perform some act to make them (ritually) clean. A side effect of the cleaning ritual is that you have all these sacrificial (and really valuable in the society in question) carcasses to dispose of. Burn a few of them and show the bodies to make sure that the serfs don't want them back and to have the nasty smell cover the fact that you are cooking the rest of them. Eat in private. Use a powerful imaginary friend for security and voi-la, you've got Levites. It's their gig for a few thousand years.
I find this a pretty plausible scenario.
So how, exactly, does God know that She's NOT a brain in a vat? 
