They alone in this world are endowed with the highest wisdom who are firm in their conviction of the sameness and birthlessness of Atman.

Non-dualistic orthodoxy is based on the form. Thus it is conduct oriented and trying to prove the truth on the base of scriptural authorities, whereas the ultimate truth is based on the soul, the innermost self.  Ultimate truth has to be proved on the base of soul-centric reasoning without the scriptures.

Orthodoxy holds the caste, religious rites, god and guru glorification, scriptural studies, virtues, good deeds and physical conducts as the means to acquire the self-knowledge, whereas in pursuit of truth, only intense urge to know the truth, receptive mind, sharpness to grasp, courage to accept the truth and reject the untruth are necessary.

The guru is needed in only in religion and yoga.  In pursuit of truth there is no need for the guru. Gnani will never accept himself as guru nor does he claim himself as a Gnani.   One who accepts himself as guru does not know the truth. When one inquires in to the nature of the mind or universe    than the truth will start revealing on its own.

That is why Swami Vivekananda said: - “You have to grow from the inside out. None can teach you, none can make you spiritual. There is no other teacher but your own soul.”

 

There is nothing more rational, more intelligible and more un-dogmatic insights of Sri, Sankara, is to drop all the theistic non-duality or Advaita which is meant for those who are incapable and not receptive to realize the ultimate truth or Brahman

Gaudapada says: - the merciful Veda teaches karma and upaasana to people of lowerand middling intellect, while jnana is taught to those of higher intellect.

According to Advaita Vedanta, the Veda addresses itself to two kinds of audiences - the ordinary ones who desire the transitory heaven and other pleasures obtained as a result of ritual sacrifices, and the more advanced seeker who seeks to know Brahman. Thus, the purva mimam.sa, with its emphasis on the karma kanda of the Vedas, is meant for the first audience, to help lead its followers along the way. However, the Vedanta, with its emphasis on the jnana kanda, is meant for those who wish to go beyond such transient pleasures. 

Sri, Sankara says in Brahma Sutras: that Brahman is the cause of the world, whereas in Mandukya he denies it. This is because he says that at the lower stage of understanding, the former teaching must be given, for people will get frightened as they cannot understand how the world can be without a cause, but to those in a higher stage, the truth of non-causality can be revealed. 

Sage Sri, Sankara himself has warned us not to use ambiguous words, and to practice semantic analysis in his book "Definition of one's own Self. [" Page 199, v.24 of "Sankara's Selected Works]

Sri, Sankara founded his Advaita Vedanta either on reason independent of sruti or on sruti confirmed by reason."   Sri, Sankara's commentary on the Mandukya Upanishad, II, 1:  This [the unreality of duality] is borne out by the Srutis ... But it is possible also to show the unreality of the object world even from pure reasoning, and this second chapter is undertaken for that purpose.

 Sri, Sankara himself had often said that his philosophy was based on Sruti, or revealed scripture.  This may be because Sri, Sankara addressed the ordinary man, who finds security in the idea of causality and thus in the idea of God—and Revelation is indispensable to prove the latter.  He believed that those of superior intelligence, have no need of this idea of divine causality, and can therefore dispense with Sruti and arrive at the truth of Non-Dualism by pure reason. 

Sri, Sankara, in debates with Buddhists and others who did not recognize the authority of the Vedas, had been obliged to prove the truth of Advaita by means of reason alone.  Mandukya Upanishad, a scripture which appealed to reason to the exclusion of Revelation. 

Non-duality does not need the support of any Scripture or Revelation like the Veda. For it is based, not upon the varying theological fancies, which are as numerous as the sands of the sea, but upon reason, the common heritage of all mankind, irrespective of colour or creed or clime.

Upanishad says:

  This Atman cannot be attained by the study of the Vedas, or by intelligence, or by much hearing of sacred books. It is attained by him alone whom It chooses. To such a one Atman reveals Its own form. [Katha Upanishad Ch-II -23-P-20]

Mundaka Upanishad  :-

This Atman cannot be attained through study of the Vedas, nor through intelligence, nor through much learning. He who chooses Atman—by him alone is Atman attained. It is Atman that reveals to the seeker Its true nature. [3 –page-70 Mundaka Upanishad  Upanishads by Nikilanada]

When the Upanishads say:-

It is attained by him alone whom It chooses. To such a one Atman reveals its own form.  Then what is the use of indulging through our intelligence or our accumulated knowledge, when one is not chosen by the self, which is the soul, which is in the form of consciousness.

There is no need for any philosophy in pursuit of truth because they take the seeker nearer to truth but they create more doubts and confusions.

 

The scriptures and theories and teaching based on the ego are not the yardstick. Using them as yardstick to understand and assimilate the truth will lead one towards pursuit of arguments. Seeker of truth has to discover on his own, the truth of his true existence by inquiring “what is mind?” and “what is substance of the mind?” and move forward.  

The ultimate truth is one without the second, the one is not in the sense half or two, but the one that remain forever One, without the second.  The consciousness is all pervading. There is no place where consciousness is not.

Consciousness is in everyone, consciousness is in everything .consciousness is one behind many. Consciousness alone is. It means the universe and its contents are the visible form of consciousness. And consciousness in turn is invisible form of the universe, which appears as mind.   

 

They alone in this world are endowed with the highest wisdom who are firm in their conviction of the sameness and birthlessness of Atman. The ordinary man does not understand their way. (Chapter IV — Alatasanti Prakarana 95-P-188 in Upanishads by Nikilanada)

Therefore, if one is seeking truth he has to know his true self is not physical but is the consciousness, which is in the form of consciousness.  

Self-knowledge or Brahma Gnana or Atma Gnana cannot be attained by study of the Vedas and intellectual understanding or by bookish knowledge.  Therefore there is no use of studying the Vedas and other scriptures in order to acquire the non-dual wisdom.  That is why Buddha rejected the scriptures, and even Sri, Sankara indicated that, the ultimate truth lies beyond religion, concept of god and scriptures. 

Thus it is necessary to follow the formless path dropping all the accumulated baggage and move forward to reach the destination in lesser time and effort.