Only lawful and neutral (not chaotic) creatures are harmed by the spell.
The spell deals 1d8 points of damage per two caster levels (maximum 5d8) to lawful creatures and staggers them for 1d6 rounds. A staggered character can take only partial actions. A successful Will save reduces the damage by half and negates the stagger effect.
The spell deals only half damage against creatures who are neither lawful nor chaotic, and they are not staggered. They can reduce the damage by half again with a successful Will save.