Sage Sankar 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.+

Many people quote Advaita without understanding it really in its highest aspect. One who follows the path of Advaitic orthodoxy is taken the path of ignorance. "How does he know that what Sage  Sankara says is true?  There are conflicting teachings. People get  confused as to which are true?" People will be unable to prove it because they do not know the proper test of truth.

Sage Sankara founded his Advaita Vedanta either on reason independent of sruti or on sruti confirmed by reason."

Sage Sankara's commentary on the Manduka 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.

Sage Sankara himself had often said that his philosophy was based on Sruti, or revealed scripture.  This may be because Sage 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.   Sage Sankar 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. 

Sage Sankara gave out what was of most use to the greatest number of people. Therefore, in the commentaries on the Upanishads, such as the famous Manduka, he gave the highest non-dual message of the identity of Atman and Brahman, revitalizing the philosophy and practice of Advaita, while in the commentaries on the Brahmasūtra he gave lesser teaching, positing both higher and lower Maya and higher and lower Brahman (Ishvara) to explain the creation for those of lesser intellects until they were ready for the highest truth. 

Remember:~

Sage 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.

According to Advaita Vedanta, the Veda addresses itself to two kinds of audiences - the ignorant people who desire the transitory heaven and other pleasures obtained as a result of ritual sacrifices, 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. Thus, All the theistic Advaita is meant for the ignorant populace.

The serious seeker who is seeking the truth is nothing but the truth or Brahman or God the Vedanta, with its emphasis on the jnana kanda, is meant for those who wish to go beyond the form, time, and space to realize their true existence is formless, timeless and spaceless existence.

All the theistic Advaita belongs to religion it is nothing to do with Sage Sankara’s Advaitic wisdom

Sage Sankara Advaitic wisdom is purely based on soulcentric reason and independent without the support of any scriptures.

Sage Sankara:~ “This (the unreality of duality) is borne out by the Srutis ... But it is possible also to show the unreality of the objective world even from pure reasoning. (Commentary on the Manduka Upanishad, II, 1)

Sage Sankara himself had often said that his Advaitic wisdom was based on Shruti or revealed scripture. This may be because Sage 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 Shruti and arrive at the truth of Non-Dualism by pure reason.:~Santthosh Kumaar