User blog:RunicVamp/Source of Magic?

Has it been stated anywhere in the series where magic comes from and why it's so powerful?

For instance: Death was bound several times with magic, despite being one of the oldest and most powerful entities in existence. Also, Rowena used a spell to remove the Mark of Cain and release The Darkness. Was The Darkness bound with magic in the first place? Is magic simply a way to tap into the energy of the cosmos (or God)?