Vedanta says that besides the body and the mind there is a third dimension to our personality-the Atman, the eternally pure, ever-conscious, and everfree spiritual dimension in us. This spiritual Reality is the substratum of the three states of consciousness-waking, dream, and deep sleep-and provides continuity during deep sleep.
"This Atman is Brahman" (Mandukya Upanishad, 2) is one of the four Vedantic equations that speak of the oneness of spiritual Existence. This statement means that Atman, the spiritual Reality behind the body and the mind, and Brahman, the spiritual Reality behind the universe, are one and the same. A spiritual seeker realizes this identity only when he knows that his true Self is the Spirit. Spiritual Reality transcends time, space, and causation, which account for our empirical existence in the world. All forms of God are manifestations of the ultimate Reality, Brahman. The Upanishads emphatically declare that by realizing this truth in one's heart-purified of all desires and free of all doubts-one transcends death and becomes immortal. (Katha Upanishad, 2.3.15) Not that the body continues to exist forever. Being born, it has to die. But a knower of Brahman becomes one with Brahman (Mundaka Upanishad, 3.2.9) and is not affected by the fall of the body.
Sri Ramakrishna's life demonstrates that God exists, can be realized, and that God-realization is the goal of human life. Sri Sankara makes it clear in his celebrated work Vivekachudamani (4) that he who does not strive to realize the Atman despite having a human birth verily commits suicide, since he kills his higher self by clinging to unreal things.
Yudhishthira's answer to the question "What is the news?" is a thought-provoking one. All created beings, he says, are cooked by time in a cauldron of great delusion. As long as we are in delusion we are in the domain of time and get cooked by it. What is this delusion? What is its source? The mother of all delusion is to believe that we are the body. This basic belief makes the external world and its enjoyments seem to be the only reality. How do we, who are essentially Spirit, believe that we are the body? Sri Shankara attributes this to maya, the power (shakti) that both conceals Reality and distorts It. Avarana-shakti conceals the spiritual Reality from us. Sri Ramakrishna would hold a towel in front of his face and ask whether those before him could see him. Similarly, he would say, we are not able to see God because of the veil of maya. Vikshepa-shakti distorts our perception of the spiritual Reality. It makes the Real appear as unreal and the unreal as Real. It makes Brahman, the Reality, appear as the world with its varied creations.
Hence it is clear that, essentially, the I-am-the-body idea is the root cause of all ignorance. The feeling of "mine" regarding things in the world stems from this idea, as Sri Shankara explains in his commentary on the Katha Upanishad (1.3.12): "Alas, how unfathomable, inscrutable and variegated is this maya! Every creature, though in reality identical with the supreme Reality and instructed as such, does not grasp the fact that 'I am the supreme Self.' On the contrary, even without being told, he accepts as his Self the non-selves-the aggregate of the body and senses under the idea 'I am the son of such a one,' though the latter is an object of perception (and hence not the Self)."
Delusion, again, is part of a graded series described in the Bhagavad Gita (2.62-3): "Brooding over sense objects, one develops attachment to them. Attachment gives rise to desire (to possess the objects). Desire results in anger (towards obstacles to its fulfillment). Anger creates delusion. From delusion follows loss of memory (of one's spiritual nature). This leads to loss of buddhi (discrimination), which leads to spiritual death." In short, it was brooding over sense objects that triggered the systematic downfall leading to spiritual death.