Meaning: That which knows everything that happens in the waking, dream, and deep-sleep states, That which is aware of the presence or absence of the mind and its functions, That which is the essence behind the ego, is the Self.
Comments: Self is, “Impersonal Awareness”. If you find it difficult to understand, it is because your mind has the wrong notion that you are body etc. So, your mind wonders how can somebody be awareness and finds it difficult to digest. The process of Self Inquiry makes the mind rethink and eventually Self is recognised directly.