The priest casting this spell instills courage in the spell recipient, raising the creature's saving throw rolls against magical fear attacks by +4 for one turn. If the recipient has recently (that day) failed a saving throw against such an attack, the spell immediately grants another saving throw, with a +4 bonus to the die roll. For every four levels of the caster, one creature can be affected by the spell (one creature at levels 1 through 4, two creatures at levels 5 through 8, etc.).
The reverse of the spell, cause fear, causes one creature to flee in panic at maximum movement speed away from the caster for 1d4 rounds. A successful saving throw against the reversed effect negates it, and any Wisdom adjustment also applies. Of course, cause fear can be automatically countered by remove fear and vice versa.
Neither spell has any effect on undead of any sort.