You use essence to empower your will.
Prerequisites
Constitution 13 or veilweaver level 1.
Benefit
You can invest essence into this feat.
You gain an insight bonus on all Will saving throws equal to 1 + the invested essence.
You gain 1 point of essence.
Special
Empyrean Will can be used in place of the Iron Will feat to qualify for a feat, prestige class, or other special ability.