You cannot raise faith above 30 without becoming a priest.
At 10 '''faith''', you may [[Exorcism|desecrate]] [[altar]]s.
At 30 '''faith''', you may travel to the [[Altar of Three]](WL) or the [[Bone Altar]](BL) (depending which of the [[Gods]] you follow) and become a [[priest]] of your god. If you're on the Freedom server, you'll need to find a priest from your religion with 40 faith to perform a ritual for you in order to become a priest yourself.