Faith Armor

This spell brings into being a shadowy, translucent armor around the caster. The aura of this roiling magic can neither be removed nor cast on other beings. Faith armor temporarily makes the caster AC 0 (regardless of encumbrance. Dexterity, and whatever real armor or garb is worn beneath it). Further, it can be set during casting to render the priest immune to the effects of all wizard spells of a particular school or all priest spells of a specific sphere, so that the armored caster is unaffected by such magic.

The material component of a faith armor spell is a handful of powdered obsidian, enough to completely cover both of the caster's palms if it is spread out as thin as dust.