Cliffy,
I'm going to assume you want an actual answer here, and that you're at least willing to hear from someone other than Motar and cj44.
Religions exist to fulfill various emotional needs in people, mostly reassurance from fear. Everybody's exact emotional makeup varies, but people with sufficiently similar emotional makeups can group together without too much friction, satisfying their belonging needs and fear of being alone.
Broadly speaking, people with a great deal of generalised fear of everything will prefer monotheistic religions with big, powerful Daddy gods who love them oh so much and are going to send everybody who scares them off to eternal torture. People with less fear will prefer more intellectualised, philosophical religions. People who view the world as compartmentalised will prefer polytheism with specialist gods. That view is in decline, so is polytheism.
You might expect that this would lead to a nice, smooth spectrum of religions from paranoid ranters with and all-powerful, vengeful god to pretty secure people with a calm, confident view and a Cosmic Muffin sort of generally overseeing the multiverse. But remember, we're dealing with poorly understood and generally unacknowledged fears here, which rarely lead to rational outcomes. Because there is enormous emotional pressure to follow the religion of one's group, few people ever change religions. If they change, they generally change within the umbrella of their community's religion. Hence, Christians have hellfire-and-damnation thunderers, religious imperialists, highly centralised structures, highly decentralised structures, quiet reassuring sects, and pacifist sects. All within the umbrella of Christianity. Muslims have Wahabis, Sufis, Salafis, and dozens of other sects of equally varying outlook.
So once you pick your sect (itself a painful process), you then get into a reinforcing loop. And your sect's philosophy will reflect, and reinforce, your fears. If you have high fear levels and a desperate need to be right, you'll pick a militant, intolerant sect. If your fears don't break that way, you'll be in a quieter, less pushy sect. And wherever you end up, you'll cherry-pick your religious text for bits that reinforce your own sect's outlook. Never hard to do, since the religious texts are an accurate reflection of the unacknowledged fears to which they respond: chaotic, internally inconsistent, and lacking in a clear and coherent message.
Politics is similar, because it's driven by the same factors. You pick your party based on what soothes your fears most effectively, then the branch of your party based on the contours of your particular outlook. Then you filter incoming information to find that which reinforces your choice.