The waking or dream is state of duality. All the three states are states of ignorance.

Sage Sri Sankara –VC "As layers of clouds generated by the sun's rays cover the sun and alone appear(in the sky), so egoism generated by the Self, covers the reality of the Self and appears by itself." 

Sage Sri Sankara –VC--"All this universe which through ignorance appears as of diverse forms, is nothing else but Brahman which is absolutely free from all the limitations of human thought

Sage Sri,Sankara said:- Talk as much philosophy as you like, worship as many gods as you please, observe ceremonies and sing devotional hymns, but liberation will never come, even after a hundred aeons, without realizing the Oneness.

The waking or dream is state of duality. All  the three states are states of ignorance.  When one becomes fully convinced that, the  self is neither the waking entity nor the self is dream entity but the self is the formless soul, which is present in the form of  consciousness than  the ignorance vanishes and reality revels itself.  

In this realm of the ignorance the universe exists as reality. the universe is the  realm of duality. In the realm of  duality  the body, ego, world,   thoughts, feeling and  perception are experienced as reality. If the self is not the  waking entity (form) than  the body, ego, world,  thoughts, feeling and  perception  are falsehood because the self is formless.  on the standpoint of the soul, the innermost self there is no second thing exists other than consciousness.  Hence it is  non-duality.  Consciousness   is ultimate truth  or Brahman.

Spiritual maturity is required  to acquire Self-knowledge or Brahma Gnana or Atma Gnana. the Seeker has to indulge in deeper self-search to understand, assimilate and realize the non-dualistic or Advaitic truth. it is possible to acquire Self-knowledge or Brahma Gnana or Atma Gnana only through perfect understanding and assimilation of 'what is truth' and 'what is untruth'. 

Only when one becomes soul-centric than  he  has the yardstick  to know 'what is real'  and 'what is unreal' and he  will be able to mentally  reject the unreal.   when  ignorance vanishes, then  non-dual wisdom dawns.

By realizing the three states are mere mirage created out of soul or  consciousness; the soul, the innermost  self  is free from experiencing  the illusory experience of   birth, life, death and the world as reality. 

In the realm of ultimate reality there is no  scope for  ignorance thus there is no duality.   Self-knowledge or Brahma Gnana or Atma Gnana destroys ignorance from its very root. 

Sage Sri, Sankara says the world is illusion, it includes birth, life and death, which happens within the world.  Thus the seekers main aim is to mentally trace the formless substance of the illusion, which is also the witness of the illusion. The formless substance and witness of the illusion (world) is the Atman, and this Atman itself is Brahman. 

 This Brahman cannot be attained by indulging in egocentric religious orthodoxy. The knower of Brahman is Brahmin not the Brahmin who indulges in priest craft, which leads one to utter darkness as per Yajur Veda. 

 

Brahmin is the one who has realized the Brahman (ultimate truth) and helps fellow seekers towards inner path. The one who knows Brahman knows his body and his experience of the world are mere illusion and also he knows his body and his experience of the world are also as Atman [consciousness], which is Brahman.  Thus, the priest craft which are crafted on the body based theories will lead one to hallucinated moksha. But real moksha or freedom is possible only through Self-knowledge or Brahma Gnana or Atma Gnana .  

Thus it is necessary to follow the path of Brahman not the path of the orthodox priest- craft. Only by   dropping all the accumulated priest crafted baggage, one has to move forward to reach the non-dual destination in lesser time and effort.