In the world of Project Eternity, different people/groups access the power of their souls in different ways, so there's one source but different techniques for accessing it. The developers want there to be mechanical differences between how the classes use these abilities.
Unlike many fantasy settings, there is very little access to curative magic. Remedies for health problems often have only a palliative or placebo effect at best, owing their continued use more to folk beliefs and tradition than any basis in scientific methodology. Though soul-based magic has helped the great exploring cultures from suffering massive pandemics and has helped some individuals overcome illness over the long-term, there is no quick magical "cure" for disease or illness. Most people go through life and death in the ordinary way -- unless they put themselves in harm's way, that is.
- 2012-25-09, Obsidian Entertainment Kickstarter Comments . Obsidian Entertainment, accessed on 2012-09-26