Whisperers are known to use their associated god's grace to accumulate Power in their own body (even if their god is just an abstract idea of a concept - whisperer's commitment is what matters first). They spend a lot of time learning how to shape it to their will, and their teachings are often reflected on how they use their spells.
Independently of their selected god, all whisperers are usually able to cast this spells in some shape or form: