A Sanctuary spell causes other creatures to ignore the existence of priest.
Unlike the 4th-level mage spell Improved Invisibility, Sanctuary does not grant a +4 to-hit bonus when attacking, nor does it grant a thief backstab damage unless they also use Hide in Shadows while Sanctuaried.
When the priest casts a Sanctuary spell, it causes all of his opponents to ignore his existence as if he were invisible. While protected by this spell, the subject cannot take direct offensive action without breaking the spell, but may use non-attack spells or otherwise act in any way that does not violate the prohibition against offensive action. This allows a warded priest to heal wounds, for example, or to Bless himself. The priest may not cast spells on other creatures without ending the spell.