Illusion means that one knows the unreality of a thing only when it disappears

One does not perceive an object as it really is in truth, but only as it appears through the screen of imagination.

 Illusion means that one knows the unreality of a thing only when it disappears. When one knows these three states are continuously appearing and disappearing, he may perceive its unreality. As one goes deeper inquiry he becomes aware the consciousness is in process of changing every moment, to moment. 

Death is but an idea within the waking/dream. It is connected with the body of the waking/dream. Waking/dream comes and goes. But that which sees the birth, life and death within the waking/dream is the Atman,which is in the form of consciousness  is  the true self. The true self is immortal.

Knowledge does not destroy the world with in the waking; it only destroys its unreality—because everything is Ataman.

 Knowledge of the dream world, which does not destroy the dream world; it shows that everything is mental or unreal.

Because of one’s attachment to the body, and his identification with it, he does not   feel this waking to be unreal. Not having inquired one is unaware of the fact that the body and the world are within the waking/dream and waking/dream are of constantly changing in their nature. One has to take the Witness-attitude to see the three states as fleeting appearance. 

Waking experience is continuously presenting with changing conditions. Whatever is within the waking experience may appear to be real and existent. It is a mistake to think that mental creations are seen to be unreal and non-existent. 

One knows most intimately and directly of his waking experience; whatever seen, known, believed, experienced of the world are within the waking experience. One is first aware of the existence of his body and the world in waking experience. 

People mistake and have impression that how can external world be illusion, when they are experiencing it.  They say they are born and living and they are going to die in it.  Suppose one is born, living and going to die in dream world, which is as real as the waking world, he will find it as reality until waking takes place.  Same way the waking world in which man exits is reality until wisdom dawns. One can call it illusion only when the non dual wisdom dawns. Until then he experiences the duality as reality.

 The world does exist as reality, but it exits within the waking/dream. But the existence of waking/dream is mental. The waking is illusion on the standpoint of its formless witness/soul. 

As nobody has ever seen the beginning of the three states, nobody can ever see its end, and hence it cannot be mortal. This does not refer to things in the waking/dream, those one does see have a beginning and an end; it refers to the waking/dream as a whole.

The idea of time is within the waking/dream; of seeing this at one time and that at another; time does not touch the perceiver. It is mirage. 

It is impossible to get to the knower, the formless witness, before it is understood that the three states are mere mirage.

The Atman or consciousness  itself is the Formless Witness: it can never be seen. One knows nothing of it directly.  The three states come and mind goes; they do not really exist. Nothing external to the formless witness exists. The three states come and goes are external to the Formless witness.  That which saw knows this is the real self: the Formless Witness; the rest is mirage. To perceive this requires a special sharpness and receptiveness. 

Non duality is of the nature of the essence of the soul or self. The ego/physical self dies daily in dream: because change identities there, as present, or billionaire and in deep sleep. The ego of childhood is dead too; thus ego changes constantly, and yet one mistake it for a reality, that which perceives the ego is the unborn, the unchanging reality. 

The three states is what the self knows, what it perceive; perceiver is distinct: three states  is an object; self is not an experience/state.