You can serve one of five, and each offers different perks in the form of spells. Spells are used for any number of things, from attacking enemies to creating creatures to help you maintain mana, guard you, and help you fight. Between juggling spells and missions and battling enemies, there's a lot going on. It's tempting to just stand still, because Sacrifice is absolutely gorgeous. Light streams through a sunset sky, multi-colored lights swirl as spells are cast.
Spells are always a great excuse for graphics fireworks.