Consciousness is that which knows everything, that which sees. Consciousness alone remains after one gets rid of ignorance. Consciousness is only the witness; it is not ultimate truth that is an error. It becomes ultimate truth or Brahman only after deeper inquiry.
The duelist sages approach was more practical, and they stuck with the reality of the world, they took it as real.
The dualist sages are unaware on what standpoint the world is real and on what standpoint the world is unreal.
The world is real because it is a manifestation of consciousness, but is unreal, in the sense, that it is not absolute and eternal like consciousness itself. Thus from the ultimate standpoint the world is unreal. Therefore whatever seen, known, believed and experienced as a person within the practical world is bound to be unreal from the ultimate stand point.
Dualist sages could not distinguish between ‘I’ and ‘formless witness.’ The 'I' was the witness. Their highest was the Jiva. One is so much attached to the 'I' that he does not want to think that 'I' does not exist. Again one is unable to detach the ‘I’ from the Real witness.
The dualist object: - If everything else is false than the statement I am Brahman is itself false, the but when one says non-duality is false, there must be the awareness, consciousness, behind the very statement. You will also go, die. One has to rely upon that which is permanent. Formless witness of the ‘I’ alone is permanent. Anything that one says is a witnessed (waking), but there is the formless witness (consciousness) there before any statement could be made.
One knows of no changes in the consciousness; he knows only the changes in what is perceived by the consciousness. When one realizes the nature of consciousness he knows the Real can never change, hence never die. Birth, life, Death and the world are reality only in the region of the "duality." The duality is an object to the formless subject.
That of which one is aware and which is nearer to him is the formless witness, which is the innermost self. Yet no statement can be made about it. All words will concern ideas about it, i.e. witnessed --never the formless witness.
Without the individual self or ego one could never think. Through such thinking one is able to prove the existence of Atman, for the individual is finally identical with the Atman because the individual and experience of the world is created out of Atman which is in the form of consciousness.
If the unchanging had also been changing, then the fact of change would never be perceptible to us. The formless witness or consciousness never alters and is thus the true witness.
The formless witness or consciousness is immortal because it is formless awareness. One sees changes always within waking or dream. One never sees it in formless witness because he never sees formless witness. Thus mortality cannot be ascribed to Formless witness as we do to witnessed.
Everything of which one is aware as a person within the waking is an illusion. As the person or ego is something of which one is aware under certain conditions, it too is an illusion.
Whatever one says as a person perceiving the world within the waking experience about ultimate truth or Brahman, it is only an idea, i.e. a duality. Reason when applied to duality one can grasp it; but he can never grasp the formless witness. Reason can show mentally the existence of the formless witness, but it cannot grasp it. This is the limit of reason. But the Formless witness is always there; it cannot be known, or understood because knowing implies a second thing. But in all acts of knowledge, the formless witness or consciousness is there when one is thinking; he is therefore seeking ultimate truth or Brahman. Hence Brahman is known only in idealessness.
It is impossible to be free from consciousness, for it is impossible for any thought to arise without it. One must analyze himself and see that whenever there is it waking experience, there must be that formless witness which is aware of it. When one sees this, he knows the consciousness the innermost self. Analyzing formless witness (soul or consciousness) and witnessed (mind or the universe) is so fundamental and so difficult.