Katha Upanishad 1:2:23:- The Soul cannot be realized through hearing scholarly explanation of the discourses, not even by the intellect.

The ignorance prevents one from knowing, which is beyond form, time and space. The form, time and space are the product of ignorance. The form, time and space are present in the form of the mind. The mind is present in the form of the universe. The universe appears as the waking or dream. Till one holds the self as ‘I’ he is in the grip of the ignorance. If the ignorance is present than the duality is present. If duality is present than the illusion is experienced as reality. If illusion is experienced as reality than one is stuck with the reality of the practical life within the practical world.  

It is not the human memory is the cause of the ignorance. The human memory is limited to form, time and space. The one which is in ignorance is not the waking entity but the formless soul. It is foolish to think you are in ignorance because you and your experience of the world are the product of ignorance.  Thus without deeper self-search it is impossible to realize ‘what is truth’ and ‘what is untruth’. Without knowing ‘what is truth’ it is impossible to know ‘what is untruth’. People are stuck with some teaching or some teacher and hold them as yard stick which is the greatest hindrance is pursuit of truth. People believe that guru or mystic or priest has got so many followers and therefore there must be some truth in their teaching, is a common fallacy accepted by the mass due to their inherited samskara or conditioning. It proves only an ignorant can find a number of greater ignorant to follow him.

That is why Buddha said: - Believe nothing because a wise man said it.  Believe nothing because it is generally held. Believe nothing because it is written. Believe nothing because it is said to be divine. Believe nothing because someone else said it. But believe only what you yourself judge to be true.

A true seeker is not content with the knowledge of spiritual realities based on hearsay... he insists on the direct knowledge."

Katha Upanishad 1:2:23:-  The Soul cannot be realized through hearing scholarly explanation of the discourses, not even by the intellect.

A permanent view of world as unreal can come only after soul centric reasoning; such knowledge cannot change. Were the seeker who is sufficiently sharpness he could grasp the unreal nature of the world by soul-centric reasoning alone.  To know whole truth, one must know the whole universe, otherwise he gets only half-truth. 

 The soul is the formless substance and witness of the three states. If the formless witness witnesses the waking experience and its attention is fixed to the waking experience than the waking experience is experienced as reality. If the formless witness witnesses the dream and its attention is fixed to the dream than   the dream is experienced as reality. If the attention of the soul is on itself than it is called deep sleep in waking experience, which is the states of ignorance. If the soul consciously remains in its formless non-dual true nature in the midst of waking experience through wisdom it is called self-awareness. 

The three states are an object to the formless soul, is the subject.  The three states are state of ignorance. In all the three states the soul, the innermost self is in ignorance of its own formless non-dual true nature.   This forgetfulness is cause of the ignorance. Ignorance is cause of experiencing the three states as reality. The three states are cause of experiencing the individuality as reality.  Individuality is cause of experiencing the birth, life, death and the world as reality.  The three states are one in essence. In the realm of truth the three states are non-existent.  In self-awareness, the three states are non-existent because they are one in essence.