One cannot be aware of his body and the world; and all his individual experience (including something of the past in the form of knowledge based on purely memory also) without the consciousness. Thus, for anything to exist consciousness is the main ingredient, therefore, everything is dependent on consciousness because everything is consciousness. The diversity is reality because; one doesn't consider his body, world and his individual experiences as consciousness.
The universe is the product of the ignorance. The universe appears as waking or dream(duality) and disappears as deep sleep(non-duality). The ignorance makes one experience the illusion as reality. The waking experience is only an appearance in which the individual perceives the world as a person and it changes every moment, at no time it is unchanging; then where has it disappeared in deep sleep or when the dream experience was on. Deeper self-search reveals the fact that, the self is neither the waking entity nor the self is dream entity but the self is the formless soul ,which present in the form of consciousness. Then who is the formless soul is the knower of these three states, which comes and goes in succession.
One has to analyze the mind in waking experience then he will be able to understand this. One mistakes the body to be the matter and everything else as mind. One thinks his body is matter and he cannot understand the fact that, the body including the world (waking) is mere illusion created out of consciousness. Until he thinks the illusion as reality he remains believing the birth, life, death and world as reality. Therefore, it is necessary to know and realize the self is not physical but self is consciousness (soul) to cross the threshold of duality.
Dissolution of the mind (universe), daily in deep sleep, in consciousness (soul), as it has emanated from and in consciousness. The waking experience is converted in to dream and the dream is converted into deep sleep. One does not know this because he does not know the three states are mere illusion and again he is afraid his body and individuality and the world will go. He cannot tolerate to lose his physical existence. Constantly thinking of the birth entity has concretizes the idea of birth, life and death, thus, the physical existence has become actuality. Same way one has to think constantly of the fact that, the self is not physical but formless consciousness to dismantle the physical structure built on the baseless [(formless)foundation.
It is difficult to say body and the world as illusion within the illusion without realizing the fact that, the self is not the form but the self is formless. Only after deeper self-search one becomes aware of the existence of the formless witness, which is in the form consciousness and become aware of the fact that, the physical existence(waking) is mere mirage created out of consciousness. Therefore, whatever one knows as person of the world is part of the mirage created out of consciousness. When the mirage is created out of consciousness then how the appearance in which man perceives the world can be true.
Just as ice block dissolves into water or ornament in to gold, so the mind (universe) which has emanated from consciousness dissolves as consciousness. Thus, no second thing exits other then consciousness.
The time (the past present and future) is part and parcel of illusion. Until one thinks the self is form, he is bound to experience the time and space as reality. The only away to overcome from the form, time and space (illusion) is to realize the self is not physical but the self is formless consciousness.
People consider themselves to be knowledgeable because they have read books and well informed about the subject. But all these accumulated knowledge is not wisdom. One can’t get non-dual wisdom from accumulating knowledge.
Whether the knowledge accumulated are of the scriptures or something from more recently published books are mere pointers to truth but not wisdom. First, whether one is aware of it or not, as he reads he is imposing his own cultural conditioning, biases, experiences, and prior knowledge onto what he is reading; this is how his thinking faculty works. He “makes sense" of new things by associating them with things he already knows.
Most of the time, this is useful. But if the "new thing" is utterly different from anything one has been exposed to before, he is almost certain to distort it to make it fit into pre-existing conceptual boxes. So much of knowledge is about changing perspective, but that's hard to do when he is twisting the knowledge around to fit the perspectives he is already has.
As one goes on digging mentally and on more things will be revealed to him through inner revelation, which makes him get a firm conviction of what is what.
One has to mentally grasp the existence of the formless witness (soul or consciousness) of the three states to realize the three states are mere illusion. And mentally focusing attention on the formless witness constantly one will be able to establish the reasoning base on the base of formless witness(soul). And when the reasoning base is established on the base of formless witness it becomes easy to understand and assimilate the self-knowledge or Brahma Gnana or Atma Gnana.
But it takes much time to establish in consciousness because one has to overcome the physical conditioning by realizing the self is not physical but it is formless.