The Soul is the essence of conscious life, whether Divine or Mortal. All Souls come from the Light of Haven, the bright ball of energy from which all of creation sprung. For every life that is born, a pure soul is taken. When a life ends, their soul is cleaned in Purgatory before being returned to Haven.
Lucef taught the Humans how to trap and harness the power of Souls. However they harvest faster than Purgatory has power to clean the Souls, and rumor has it that a darkness has crept into the Light of Haven, and that new souls do not always come out pure anymore.