http://Dictionary.reference.com/ defines Faith and Peity as such…
faith [feyth]
noun
1. confidence or trust in a person or thing: faith in another's ability.
2. belief that is not based on proof: He had faith that the hypothesis would be substantiated by fact.
3. belief in God or in the doctrines or teachings of religion: the firm faith of the Pilgrims.
4. belief in anything, as a code of ethics, standards of merit, etc.: to be of the same faith with someone concerning honesty.
5. a system of religious belief: the Christian faith; the Jewish faith.
pi·e·ty [pahy-i-tee]
noun, plural pi·e·ties.
1. reverence for God or devout fulfillment of religious obligations: a prayer full of piety.
2. the quality or state of being pious: saintly piety.
3. dutiful respect or regard for parents, homeland, etc.: filial piety.
4. a pious act, remark, belief, or the like: the pieties and sacrifices of an austere life.
How to Join a religion:
Acts of Piety
Anyone can say they are part of a religion or worship a particular god, but truly doing so requires faith. Piety can be real or feigned, but faith cannot. Those who truly believe are willing to show their inner Faith through an outwards act of Piety. These religious ceremonies could be simple and harmless or complicated and dangerous. The greater the complexity and danger the stronger one's faith is tested, but the fewer who will pass this test. As such, gods rarely make these acts of piety difficult for the newest of worshipers. Those seeking a greater connection to their god, though, and thus greater power, often must undergo great tests of their faith.
Anytime someone begins to show interest in a religion or deity they are called a follower. Then, when they are ready, they may choose to become a worshiper, or as some call it a "believer".
Joining a religion usually takes three Acts of Piety:
1) Admission and Confession: Admitting before an audience that one believes in this religion. This may also include confession of sins, as perceived by the faith.
2) Initiation Ceremony: An act of piety demonstrating ones belief and faith before religious leaders or other worshipers.
3) Indoctrinization: Being educated in the core beliefs of the faith.
Upon completing these three Acts of Piety a Follower becomes a Worshiper.
Admission and Confession:
Initiation Ceremonies:
It is important to understand that those who truly believe, worshipers, are bound to their deity. Their souls are quite literally connected to that deity. As such they are guaranteed a place in the after-life of that deity, or whatever reward that deity offers for the faithful. However, they are also subject to the wrath of that deity and as such if the deity finds them to be unworthy they can be punished in the after-life. Once this connection is formed it is difficult to break, because it requires that one either become profoundly devout to another deity or religion, or truly have lost faith in the religion they were bound to. Losing faith isn't as easy as it sounds. If one believes that deity has dominion over their soul, it is hard to let that go, even when one has acted contrary to that deities commands. The GM should not allow someone to end their connection to a particular deity or attain worship of another on a whim. This act should require serious role playing and lengthy period of time. In the end the character should demonstrate a crisis of faith, a shattering of conviction, and -if joining a new religion- an overwhelming conversion both mentally and spiritually to the new faith.
Remember, the gods can be generous, but they can also be wrathful. Those who begin to break their ties may find themselves at the wrong end of god's ire. The more powerful and well renowned the believer, the greater that wrath will be.
Indoctrination into a Faith:
Worshiper's Abilities:
Worshipers are rewards by the god or pantheon with the rite to call upon the deities for aid. In most cases this is a minor power, often inobvious, but useful and demonstrative of the deity's power.
Example: Worshipers of the Ronan Religion have the power of Divine Protection against Evil. This power requires the use of a holy symbol and the invokatin of the deity's name. When invoked the power causes a 10' radius invisible barrier to form around the worshiper that prevents any creature of evil alignment from entering the area without making a willpower save vs a DC of 12. The sphere of protection lasts so long as the worship concentrates upon this and nothing else. Concentration can be broken and this power does not deflect any projectiles or magic. Evil creatures who fail the save may not attempt to break through again for 24 hours. The power can only be used once per day. Multiple worshipers may combine their faith. For each additional worshiper the sphere is expanded by 2 feet and has a +1 to the DC. Thus, 11 worshipers would have a 30' radius of protection with a DC of 22.
Priests and Prophets and Warriors of Faith
Priests
Prophets
Warriors
Crusaders
Inquisitors
Paladins
Rangers
Faith Zones
The power of the gods is limited by the faith in that deity in the region. This is reflected by how easily Priests and Warriors of Faith access the power of their deity. In areas where the faith is strong they have easy access to their powers (no Caster level mod), but in places where other religions are more prominent it can be very difficult to access the power of the deity (-1,-2 or even -3 caster levels). In rare situations, faith in a pantheon is so great, so zealous that casters actually find it far easier to access the power of their deity (+1 caster level).
Prophets are the only exception to this rule. Because they are unquestionable believers with a direct connection with their deity they are never affected by the faith of others. This is why the are so great at bringing new believers to the faith. Even when no one else in an entire realm believes in the power of their deity they can perform miracles.
Example:
Ronan Pantheon Faith Zones
+1 CL Mod Sora
0 CL Mod Rona, Moar, Gand
-1 CL Mod Parthus, Gelvani Realms, Duervan Realms, Bamoria, Kamora, Skarrellands
-2 CL Mod Kal-Mikan,Vas-Meknor, Ogre Kingdoms, Ryosha, Valderheim
-3 CL Mod Beyond the borders of man