What is accepted without proper inquiry will not lead a person to the final goal

As one goes deeper in self-search one becomes aware of the fact that, Vedas including Upanishads considered being supremely authoritative, as revealed truth.  But Upanishads clearly declares that:-

 Katha Upanishad delares:-

  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 page70upanhsds by Nikilananda)

 

It means the truth is beyond scriptures and egocentric intelligence.  Thus in order to grasp, assimilate and realize the non-dualistic truth the seeker to employ soulcentric reasoning faculty.  

That is why Sri, Sankara says in commentary in Vedanta sutra that: What is accepted without proper inquiry  will not lead a person to the final goal. On the contrary, such acceptance will result only in evil, in something which is detrimental to our spiritual progress.   Seeker of truth should not believe blindly in traditional orthodox non-duality without verifying all the facts from every angle. One has to reflect through reasoning over and over again without getting tired of the process.