Creeds in Salt and Sanctuary are factions that the player can align with to bestow certain benefits and different NPC merchants in their Sanctuaries through the use of Offerings. NPCs will sell different gear depending on the Creed. Some Sanctuaries are occupied by Creeds that are different from your own, where you cannot make Offerings without desecrating them with a Stained Page or by using a Crystal Sphere to convert them; however, you can still level up and view the Tree of Skill.
You can also convert to that sanctuary's creed if desired (so long as you are not an apostate to that creed). Desecrating a Sanctuary of another Creed will give you Sin and will turn any NPCs in all Sanctuaries under that creed hostile to you. You will also have to defeat multiple waves of difficult enemies (which for now are being called Sanctuary Guardians) before you are able to convert the Sanctuary to your Creed and use its services. Abandoning a Creed for another makes you an Apostate. There are 7 Creeds in Salt and Sanctuary. Endings are affected by your Creed.
Devotion & Sin
Creeds have Devotion. To raise your Devotion level, you must turn in remains from Enemies to a Stone Leader. Each time you raise your level of Devotion with a Creed, you will be able to select from a list of rechargeable items of your choosing as a reward to the player. The first two items always act the same as standard HP and Focus potions, albeit with differing stats depending on the creed, and can be replenished at a Sanctuary belonging to that Creed. The last two items tend to be more creed-specific, but usually involve rechargeable buff items. Additionally, NPC vendors will start selling new items at higher levels of devotion. The max level of Devotion is 7.
If you choose to leave your character's Creed to join another, you will gain Sin and become an apostate to the Creed you left. Your devotion to that creed will be reset to 1, and you will not be able to rejoin that creed again unless you cleanse your sin by giving salt to the Candlelit Lady (roughly 1,000 salt every time you abandon a creed).
Desecrating a Sanctuary by using a Stained Page will give you Sin and make all sanctuaries of that creed hostile toward you. You will be unable to teleport to any of that creed's sanctuaries and you will be attacked upon entering. You cannot desecrate a Sanctuary of your own Creed. You can have your sin forgiven by giving salt to The Candlelit Lady to cease the hostility of creeds you have desecrated (roughly 10,000 salt per desecration). Note that taking over a sanctuary via desecration will require the player to permanently kill all its existing NPCs, meaning the player will need to repopulate it using stone idols if they desire to use vendor services there.