Brave affects physical attacks and defense. The higher the number, the better your physical offense and defense are. A low Brave makes it easier to find rare treasures by Move-Find (odds of getting the rare item is equal to 100% - Brave).
Faith affects how much damage your spells do and also how much damage spells do to you. Both healing and offensive magic are affected by Faith. Having a Faith of 0 (Innocent) makes you immune to spells completely.