Faith is a special resource unlocked with Divine Form, it is represented by a yellow bar below the mana bar. It allows you to activate Divine Form in any place, and gives you the ability to heal or break out of a stun. If you have insufficient amount of Faith, you are not able to change into Divine Form. Each transformation consumes 200 points of faith, which can be further reduced by unlocking nodes in the Temple of Deeds.
Faith can be obtained by sending Adepts on journeys and getting rid of those you do not want.