Those who have faith in the personal God will not be able to grasp the non-dualistic or Advaitic truth because they are holding on to that idea of god imagined on the base of physical self (waking entity or ego).

The soul, the innermost self has to be free from experiencing the duality as reality.  To overcome the duality, the waking entity has to know it itself is not the self but the self is the soul, which witnesses coming and going of the three states.  Thus self-knowledge or Brahma Gnana or Atma Gnana is necessary to realize ‘what is truth’ and ‘what is untruth’ to reject the untruth by accepting the truth. –FORMLESS PATH   

The consciousness is the one Truth, and a Gnani is person who had realized the soul as self, but outwardly he views worldview on dualistic standpoint.

 As a seeker one is aware of only the physical (false) aspect of the consciousness and then by a gradual process of reasoning to strengthen the foundations of spiritual (real) aspect of consciousness.

The highest principle, the self of all, cannot be a Person. The waking or dream is an individual and the sum total of all waking or dreams is the consciousness. In the waking or dream, ignorance is predominant, but consciousness controls illusion composed of ignorance and knowledge and independently projects this mind, which contains the world of moving and immovable things out of itself. 

But consciousness transcends the individual and collective aspects, the waking or dream and soul. In soul, which is in the form of consciousness there is no part. It is for the sake of easy comprehension that parts have been imagined in It.

 The waking or dream and the universe are merely mirage created out of consciousness. That the mind consists only of name and form. It endures only so long as there are names and form. When through inquiry, analysis and reasoning name and form are dissolved, and then only the transcendent consciousness prevails.

 Then the separate reality of waking or dream and the universe (mind) is felt no longer remains as reality. Then it is realized that one is the ultimate truth. The real nature of the mind   is consciousness. When the veil of name and form vanishes through wisdom, then that idea is simply realized.

By limiting the consciousness to the physical body one remains ignorant of the fact that, the consciousness is, which is true self pervades in everything and everywhere in the physical existence.  By limiting the consciousness to the physical he remains in doubts and confusion about his own formless true existence.  

 Only Through soul centric reasoning  he has to understand, assimilate and grasp the non-dualistic or Advaitic truth. Whatever he thinks on the base of physical self (ego or waking entity) is limited to the physical existence (universe or mind). 

It is the natural tendency of man to argue, from the base of the physical self (waking entity) because man and his experience of the world is the product of ignorance. The truth is beyond the physicality, therefore on having to learn to view and judge the three states  on the base of the formless soul, the innermost  self, in order to overcome the ignorance. It is necessary to analyze the three states  on the base of the formless  soul, in order to assimilate the Self-knowledge or Brahma Gnana or Atma Gnana.

Man can only think of his ideal as a human being. When buffeted by sorrow in this world of disease and death he is driven to desperation and helplessness, then he seeks refuge with someone, relying on whom he may feel safe. But where is that refuge to be found? The omnipresent soul, which depends on nothing else to support it, is the only Refuge. 

At first man does not find that. When discrimination and dispassion arise in the course of his quest for truth, he comes to know it. But in whatever way he may progress on the path of truth, he is unconsciously awakening consciousness within him. But there is no other means other than the path of inquiry, analysis and reasoning. 

Those who have faith in the personal God  will not be able to grasp the non-dualistic or Advaitic truth because they are holding on to that idea of god imagined on the base of physical self (waking entity or ego). Sincere and the serious seekers will come the awakening of consciousness within. The self-knowledge or Bramha Gnana or Atma Gnana is the goal of the truth seeker.  Various ideas are the various paths will not lead to non-dual destination. Although the real nature of the mind is consciousness, still as he has identification consciousness with the physical self (waking entity or ego), is the cause of the suffering from all sorts of doubts and difficulties and experiences the pleasure and pain as reality.

Everything within the waking or dream is a creation of consciousness. No one can escape the illusory experience of birth, life, death and the world until they realize their identity with consciousness.

When the desire for freedom becomes very strong, and along with it comes the grace of a person of realization, then man's desire for Self –Knowledge or Brahma Gnana or Atma Gnana becomes intensified. Otherwise the mind of men given to lust and greed is never inclined that way. How should the desire to know ultimate truth arise in one who has the hankering in his mind for the pleasures of family life, for wealth and for fame? 

He who is prepared to renounce the ignorance will be able to grasp the non-dualistic or Advaitic  truth. Who is immersed in strong current of the duality believing it as reality without verify the facts will never be receptive to assimilate the Self - knowledge or Brahma Gnana or Atma Gnana. He alone by the might of the sword of Self-knowledge or Brahma Gnana or Atma Gnana   will be able to break the barriers of illusion.

Without wisdom, there can be no Self- Knowledge or Brahma Gnana or Atma Gnana.  The wisdom can be got by getting rid of ignorance. Only through deeper inquiry, analysis and reasoning on the base of the soul as self the ignorance vanishes.  

Neither by spiritual practice nor by yoga nor by hearing sermons ultimate truth is difficult to realize. Without realizing the fact that, the world is an illusion, without renunciation of ignorance , without giving up the illusion which one believes it to be real , absolutely nothing can be accomplished in the path of truth. Truth is not a thing anyone can snatch by a trick."