The illusion covers and hides the Consciousness.

Until one  understand what mind  really is, he will not be able to assimilate non-dualistic  or Advaitic  truth. Consciousness is the essence of the mind and consciousness is the soul. the soul is the innermost  self not the  waking entity(ego). Considering the waking entity as self is cause of the  egocentricity.

 Consciousness cannot be divided into fragments, and Consciousness is the innermost self  self .  Consciousness is enduring, and existing in everything and everywhere  in all  the the three states.

Thoughts, ideas, experiences  and  feelings,  are part of the  illusion. The  nature of  illusion  is constant change, and in this sense are to be regarded as unreal. The illusion covers and hides the Consciousness. The illusion  seems to be reality on base of the ego or waking entity,which is false self within the false experience. 

In non-duality there is no' two', there is only 'one'. It is only illusion and on the base of waking entity or ego  ,which is the   cause of   to view everything as separate from him. This fact is discovered through deeper self-search. when one becomes aware the self is not physical but it is formless spirit  then  the fallacy of   three states is exposed.   in realm of truth  there is no second thing exists other then the spirit. thus whatever exist as universe is mere mirage created out of consciousness. thus consciousness alone is real and eternal. 

Self- Knowledge or Brahma Gnana or Atma Gnana is necessary in order to realize what is what.  To understand  and assimilate the non-duality and acquire Self-knowledge or Brahma Gnana or Atma Gnana  one has to know what is mind, because this knowledge and realization is beyond the mind.

All the three states  are mental. In order to know something beyond the mental states,  one needs to  analyze the three states. To comprehend the mind and what is beyond it, one has to rise above it, to the source beyond it.

Consciousness is the innermost Self. Consciousness is within this universe but it is not of this universe. It is in this universe, but not of this universe means it is the formless substance and witness of the universe, which is in the form of the mind (I). The mind (I) appears as waking or dream and disappears as deep sleep. The self who is in the form of consciousness is the formless knower of the mind, which comes and goes.   Consciousness is above; it is transcendental to all the miseries, which are inevitable in this illusory universe.  Therefore, there is a need to realize the fact that, the mind, which is in the form of universe is mere mirage created out consciousness.   Thus, the birth, life, death and world are mere mirage on the stand point of the consciousness, which is the true self. Only on the base of physical self the universe is reality.  Thus the Self is within the universe but it is without the universe.

Only a Gnani alone can actually create the awareness of the truth. He can enliven and illuminate others to get out of this ignorance by being transcendental to the illusory birth, life, death and the universe. Gnani tries to guide the seekers get rid of the inherited ignorance and, rise above the egocentric concepts, be in this universe, but not of this universe, be in tune with the consciousness, which is his  true identity and the ultimate truth.