Heaven and Earth
This edition of Clerical Error is about a way religion can be used in world-building. If you are trying to design a new culture, or add more detail to a pre-existing culture, please keep in mind that the religion of a people does not exist in a vacuum. Any culture's religious worldview will be connected to and reflective of other parts of their day-to-day life. When designing or running a culture, if you know the culture's religion, you can figure out a lot of other things about them.
A basic belief shared by all world religions is that there are two levels to reality. The first level is the terrestrial world, the world of physical existence. But religion teaches that there is more to existence then the world we can touch and see. There is the other level, the divine world. The realm of gods, spirits, and everything that religion describes. The point of religious practice is to connect these two worlds together. And in most religions, these two levels of reality reflect each other.
Alignment as Religion
We can see an example of the two levels of reality reflecting if we look at two societies everyone had to learn about in 9th grade world civilizations. The Egyptian society was based around the Nile River, which flooded regularly and predictably. Consequently, the Egyptians believed that the gods were rational, ordered, and oh, let's say ...lawful. The Babylonian society was based around the Tigris and Euphrates rivers, which flooded randomly. The Babylonians believed that the gods were irrational, capricious, and ... chaotic.
This sort of analysis can apply to any gaming society that fits a classical alignment system. If a culture's deities are chaotic, then that is because they see the world as chaotic. The same would apply for a lawful religion/society. If you are world-building and you know the religious alignment, it could be a good jumping off point for developing other details of their life.
If the society is "chaotic" then for some reason, they see the world as chaotic. It might be because, like the Babylonians, they are based around a randomly flooding river. Or possibly they are from a geologically unstable region, or they are from a planet with high radiation, and thus heavy mutation. Anything you can think of to explain why their worldview is chaotic will work.
Here is an example society, developed entirely from the fact that their deities are chaotic. The creatively named Chaosians developed in a region of their world that suffers the side effects of past magical warfare. The seasons are unstable--winter might follow summer or spring, or might not come at all. It might last for three days, or three hundred.
The Chaosians believe that the heavens are filled with warring pantheons of gods, based around the seasons. The Lord of Summer is ruler of a court that includes gods of fire, light, fertility, etc. The Lady of Winter is the mistress of the gods of wind, ice, night and so on. The season changes are caused by the different fortunes of the gods in their war.
The different tribes of Chaosians are devoted to different seasonal courts. They believe that they purity of their worship and obedience to their religion can strengthen or weaken their gods. The clerics are seen as soldiers of their gods, and the rituals they perform actually help to wage the war for their gods. The unpredictable seasons mean that they live a harsh, hand-to-mouth existence, and following of their ritual law is enforced brutally. There is no room for weakness or error in their world, or their religion.
Alignment as Culture
However, the worldview of a religion does not just mirror natural phenomenon; it also mirrors social structures. The way a society is arranged will be a reflection of the way the people believe the universe is arranged.
In the Middle Ages, Catholics believed that God had ordered the universe in a strict pyramidal way, with God on the top followed by angels, humans, animals, vegetables, and minerals. They believed that the social structure of feudalism--king, lords, knights, all the way down to peasants was not just a random consequence of history, but was a mirror of the divine order of the universe. This sort of social/religious paralleling can also be useful world-building tool.
To continue our example of the Chaosians, because we know about their religion, we can develop their culture. The Chaosian society is based on the idea that behind seemingly random events (seasons) there is a divine order.
So the main form of conflict-resolution would be ritualized gambling. One of the Chaosian priest's jobs would be to run this gambling. Court cases, personal grudges, political disagreements--all would be settled by gambling. The gambling rituals might take different forms, from the simplest (dice) to the most complicated (animal or human combat). Chaosian war making would also be based on their religion. The main way of waging war would be single combat by a special holy warrior class of champions.
Reverse Engineering
Of course, using religious worldview to world-build works both ways. In this example I built a culture out of a religion, but you can also build a religion from a culture. If you know enough about a people's way of life, you can also figure things out about their way of believing.
If I know that a culture is obsessed with proper protocol, then I can create a religion for them based on strict observance of ritual in every aspect of daily life. Perhaps they believe that the gods have dictated a specific way of living that they must follow in every detail, or they risk divine wraith. Perhaps they believe that by living this way they can transcend time, connecting to all past and future generations of their people. Perhaps they believe that the gods live a strictly regimented existence and that through imitation of this they may spend eternity with those gods. Knowing a single thing about their culture gives me many options for designing paralleling religious beliefs.
The religious beliefs of a culture do not exist by themselves. A realistic culture will have a basic worldview that includes physical circumstances, social structures, and religious beliefs. Their view of Earth will mirror their view of Heaven. If you know one of those things, you can use it to guide the creation or development of the other two.
Questions? Comments?

