Karma is the gauge of human morality left in a being, and is the key to getting into the afterlife. Angels gauge Karma based on a Human/Demon's actions. Positive Karma is instilled instantly to Humans and Hybrids while Negaitve Karma is automatic within Demons.
Karma is decided by the path chosen by a human. Because Angels believe their is good in everyone, Karma is never set in stone and can be changed. It is believed that humans and hybrids are always born with good Karma while when a Demon is chosen, it is turned to Negative Karma. Positive Karma allows one into the after life while Negative does the opposite after death.