One can only know the universe is a mirage, when he discriminates between the three states and the formless witness of the three states. Thus, it is necessary to understand the fact that, the formless witness is apart from the mind or universe, which appears as waking or dream experiences. When the universe was nonexistent in deep sleep it was in its formless non-dual true nature. The knower of the coming and going of the universe [mind] is birthless and apart. This has to be grasped mentally and just as one knows a sound by its contrast to silence.
The one investigation into mind, which is in the form of universe, is infinite; it will always go on and yet never come to an end. For however many things may be known, there will always be more waiting to be known. They must realize the fact that the nature of the universe is only mirage; whatever they discover within the mirage, they will only discover only mirage. Realizing this, they will have to turn to the formless substance and witness of the mirage to know the consciousness alone is real the universe is mere mirage.
When one denies existence of the soul, which is in the form of consciousness, he denies only the physical existence [universe]; consciousness is the secret support of his denial. The universe is erupted from consciousness, sustained by consciousness and finally it dissolves as consciousness. The Illustration is the dream. The dream has erupted from consciousness, sustained by consciousness and finally it dissolves as consciousness. Same way the waking experience also erupted from consciousness and sustained by consciousness and finally dissolves as consciousness.
The formless substance and witness of the three states alone is permanent, the three states goes. Those who cannot understand and analyze all experience into formless witness and three states will always have trouble in grasping the truth.
Universe or mind is mere mirage, but one cannot say it is mirage unless he becomes aware of the existence of the formless witness. It is there always, hence it is impossible to be aware of three states without it.
There can be no such thing as a three states without the formless substance and witness, which is consciousness. No one can see the limitations of the Witness i.e. the true self. If one sees his limitations, then he is seeking body as self or witness, not the true self, which is in the form of consciousness.
Universe or mind is only an object or seen, hence one try to transcend it. Even consciousness is only an idea within the mirage. The universe is mere mirage to the true self, which is consciousness. The subject [consciousness] as well as the object [universe or mind] is one in essence. Thus, everything [whole universe] is consciousness. No second thing exits other than consciousness. Hence it is non-dual.