The Light and the Darkness are each a sentient, intelligent, formless consciousness. And while they may exert a supernatural presence they lack a physical body to enforce their will. Many beings may be chosen to become a host for the Light or Darkness to spread its domain, known as avatars. Most chosen avatars maintain some semblance of their former selves in this process and so the Light and Darkness must choose its vessels wisely, those of strong will and devotion could fend their attempts of domination but they are often those most worthy to wield the power of the Light or Darkness. And while the Light would never willingly bestow its power on the dark hearted, the Darkness will take any chance to corrupt the good and righteous.