Sri, Sankara says in commentary in Vedanta sutra that 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 Ataman 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 Ataman 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 Ataman—by him alone is Ataman 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 soul-centric 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.

Scholastic explains nonduality:-

Duality and Non-duality

We live in a world of apparent duality. There is “I” and there are other people, objects, ideas and emotions. Time, space, causality and language all depend upon and relate to this world. Whilst every “thing” else changes, however, “I” who witnesses and knows all of these experiences remain the same.

This separation is grounded in our use of language. At the earliest age, we are taught to differentiate and “name” the things around us – “me”, the subject, and “something else”, the object. But these names are actually “attributes” and not things-in-themselves. We refer to a “golden ring” with “ring” as a separate noun but the ring is actually only a transient form of the gold – we should really call it “ringy gold.” Form is the “attribute” of the object and should be expressed as an adjective and not a noun. 

But gold is only a particular and temporary configuration of protons, neutrons and electrons, so that it too is an adjective or attribute. Similarly, protons etc. are themselves made up of still smaller particles, called quarks. Ultimately, everything is only name and form of that fundamental reality which is changeless – the only noun which is not an attribute of something else. 

There is a famous quotation in the Chandogya Upanishad - sarvam khalvidam brahma - all this (universe) is verily Brahman. By following back all of the relative appearances in the world, we eventually return to that from which it is all manifest – the non-dual reality.

The orthodoxy which is based on individual conduct is not the means to acquire Self-Knowledge or Brahma Gnana or Atma Gnana, because the self is not individual. The self is formless and it pervades in everything and everywhere in the universe.  Thus all this theoretical philosophy and theories based on the individual conduct are not the means to self –knowledge or Brahma Gnana.   Because the non-duality cannot be mixed with religion and yoga because in religion and yoga one has to accept blindly and there is no scope for inquiry.

  Religion is based on ego, which is the false self within the false experience whereas the ultimate truth is based on the formless soul or consciousness, which is the innermost self.

The orthodox pundits say that Vedas as final authority for the Vedantins and he has nothing else to believe in it, they do not know the fact that they themselves are indulging in non-Vedic activities which Vedas clearly bars.