When some nomads started staying put and growing some taters & turnips around 10,000 BCE they became acutely aware of the weather and they needed to contact whoever was in charge of rain and sunshine and get a little co-operation going. They figured just because you can't see something doesn't mean it's not there. So, for instance, the wind. These invisible things - let's call them spirits - were just everywhere, and they were running wild. But some people could talk to them, and make deals. You do this for us, we'll do that for you. So that was the concept of sacrifice. Here's a goat, now give me a wife. Alright, two goats. Arm-twister! Hey, don't snow all over my cabbage patch, here's a donkey.
Some of it wasn't no donkeys neither. It turns out that the grisly heads rolling down the ziggurat scenes in Mel Gibson's Apocalypto movie were factually correct. Ugh!
Some bold types called shamen took strong medicine and went across to the spirit world and returned with very specific knowledge (the necklace you lost is behind front door of your neighbour's hut - not saying how it could possibly have got there).
Oh, humans have spirits too, and the good news is, they're immortal. Actually, the land and the spirits and the creatures and the humans are all part of each other, it's like that crazy novel The City and the City by China Mieville, these different worlds all co-terminous in the same place and interweaving and all.
Well, several thousand years passed and spirits in some places became gods and got specific powers and tights and capes to wear too, and city states grew up all over, their kings were divine or divinely chosen, and the people believed that tosh because the priests told them it was true. That happened in the USSR under Stalin too, so it's an idea which took a long time to die out.
This excellent book then moves on to the oldest living religion, Hinduism, followed by Buddhism (which might not be a religion, it's much more a philosophy), Judaism, Christianity and Islam, the three great monotheisms. Finally we get a miscellaneous section which tears through Sikhs, Santeria, Mormons, Baha'I, Tenrikyo, Cargo Cults (which have now disappeared), Jehovah's Witnesses, Rastafari, Cai Dai, Scientology, Unification Church, Wicca, TM, UUA, Krishna Consciousness and Falun Dafa. They all go by so rapidly that I'm not sure the subtleties of each faith are adequately explained - the Unification Church appears just to believe that everyone should get married, for instance. I think there must be more to it than that.
But mainly the nine authors of this classy compendium can cheerfully collect compliments and congratulations for their collectively crisp, cool, calm compression of these copious complex, confusing and contrary concepts.