Sage Goudpada wrote his Manduka Karika to establish the truth of Non-duality by sheer reasoning alone.+

The seeker after the truth should take to Soul-centric reasoning and discriminate between dual and nondual experiences to realize what the truth is and what is the untruth.

Those of superior intelligence, have no need for this idea of divine causality, and can, therefore, dispense with Vedas and arrive at the truth of Non-Dualism by pure reason.

Sage Sankara says in the commentary on Vedanta sutra that what is accepted without a proper inquiry will not lead a person to the final goal. On the contrary, such acceptance will result only in evil, something which is detrimental to our spiritual progress.   

Seekers of truth should not believe blindly in traditional orthodox nonduality without verifying all the facts from every angle. One has to reflect through reasoning over and over again without getting tired of the process. 

Sage  Goudpada wrote his Manduka Karika to establish the truth of Non-duality by sheer reasoning alone. He begins by defining "What is real?" "What is unreal?" etc, because that is the right way to discuss or teach. People must first know what they are talking about. 

The path of truth is the path of verification. As one goes deeper in verification he will be able to drop all the inherited accumulated knowledge based on the birth entity (waking entity or you) such as religion the idea of God and Guru, the world, and his body.   

Because he is fully aware that, his body, his ego,  his idea of God, and the world in which he exists are merely an illusion created out of the Soul, which is present in the form of consciousness.

 
The Soul is the Self.  Thus ‘I’ base the Self on the Soul. The Soul is birthless and deathless because it is a formless, timeless, and spaceless existence. 

   
Thus, my judgment is based on the Soul, which is present in the form of consciousness because all else is merely an illusion created out of consciousness.  Thus, the whole universe in which we exist is nothing but consciousness.  

If one finds any second thing other than consciousness then he is still in the grip of duality. If one is in the grip of duality, he has not reached the ultimate end of understanding. 

People view and judge from a dualistic perspective and they fail to realize the reality, which is based on the Nondualistic perspective. 

Sage Sankara says: - VC-47- All the effects of ignorance, root, and branch, are burnt down by the fire of knowledge, which arises from discrimination between these two—the Self and the non-self.

Till you think you are an individual separate from the world and the world existed prior to you and you are born in it afterward ignorance will prevail as a reality. Till ignorance is there the universe prevails as reality.

Sage Sankara says: ~ “The exercise in discrimination between real and unreal and renunciation of the false is real meditation, then why you are indulging in other types of meditation.

Remember: ~

Perfect understanding and realization of ‘what is what’ leads to Self-awareness. By holding on to theories one remains in the realm of duality. You have to mentally go on dropping what is not the truth through deeper self-search. 

Finally, when you become aware of the fact that, your ego, your body, and the world are one in essence then there is Self-awareness in the midst of duality.

The seeker who has an intense urge to know the truth and is sharp in grasping, skills in understanding, and assimilating without the scriptures, the one who has these characteristics is the fit recipient of Self-knowledge.

People, who have not become firm in their power of reason, quote someone else as authority to support their reasoning because they have not got fullest confidence in their own powers.

When one is certain then he does not need any authority to support or confirm himself. There is no need for it. 

To appeal to other views indicates his own reasoning is incomplete. Thus,  the seeker has to do his own homework independently.

Gnanis quotes the verified citation of scriptures or sages of the past just to inspire the seekers who hold scriptures are the ultimate authority to show the scriptures or sages are saying the same thing.

The seeker must not tell a lie is the first requirement in the pursuit of truth.” What he likes in practical life is not concerned with. 

The seeker has to keep his intuitions and instincts at a distance and he has to stick to a known fact. To inquire, analyze and reason means to go to the very end of things.

Sharpness to grasp the truth is necessary for the pursuit of truth. If the seeker is sharp enough then by merely hearing the truth mentioned he will grasp it.

The seeker has to analyze the three states, and he has to think consistently about it. Exercise his thinking faculty and inquire continually; discrimination is essential; this practice is the only way to understand, assimilate, and realize the non-dual truth. : ~Santthosh Kumaar