Omniscience comes about through the elimination of the afflictive and the epistemic obscuration. Here, the afflictions are passion and so on. They are called the afflictive obscuration because they block the vision of what is real. And when a person sees the reality of that which is to be abandoned and that which is to be taken up but does not know it in all of its aspects and is not capable of explaining it to others, that is the epistemic obscuration. In that case, because one has directly realised selflessness, there is the elimination of the afflictive obscuration. But the [elimination] of the epistemic obscuration for one who has seen selflessness comes about through the intensive, continuous, and long-term cultivation [of that realisation].

-- Kamalasila