The body is like a water bubble. It will disappear one day or the other. You are not the body that has birth, growth, decay and death ultimately. Therefore, Lord Yama exhorted Nachiketa to realise the Atma that has no birth or death.
Then, the question arises as to what is the Atma? The Atma is formless, infinite, indescribable and immeasurable. It is Nirgunam, Niraranjanam, Sanathana, Niketanam, Nitya, Shuddha, Buddha, Mukta Nirmala Swarupinam (Atma is attributeless, pure, final abode, eternal, unsullied, enlightened, free and embodiment of sacredness). Such an Atma-tattva is immanent in every individual, nay in every being in the form of consciousness. Your life as a human being will acquire a meaning and purpose only when you realise the consciousness. Enquiries relating to worldly matters are meaningless and an exercise in futility. Lord Yama exhorted Nachiketa to realise that principle, having realised which he would have realised everything else. The body has birth, growth, decay and death. But the Atma is not subject to all these changes. It is the eternal witness of everything in the universe. You have therefore to realise the Atma-tattva. Thus taught Lord Yama to Nachiketa.
Lord Yama told Nachiketa to realise Atma-tattva which is real and eternal. You can recognise that Atma-tattva, not by your Charma Chakshu (physical eyes) but by Jnana Chakshu (eyes of wisdom). Then, the question arises as to what is Jnana (wisdom)? Is it physical knowledge or secular knowledge or knowledge relating to the objects of Nature? No, none of these. It is the knowledge of the Atma-tattva. Hence, attain Atma jnana (the knowledge of the Self). That is true wisdom. People adopt various spiritual practices to attain Atma jnana. They close their eyes, sit in a particular posture and call it spiritual Sadhana. But nothing of this sort can help to attain Atma jnana. What is important is Prema (love) which is the undercurrent of all forms of spiritual Sadhana. Realising the perishable nature of this Deha (body), one has to realise the In-dweller (Dehi), who is none other than the eternal Atma.
The eternal Atma-tattva is immanent within us. It can be realised in a moment if you give up Dehabhimana (attachment to the body) and cultivate Atmabhimana (love for the Atma). You think you are the body and develop attachment to it. But how long does this attachment last? So long as the process of inhalation and exhalation continues in the body, you consider it as yours. Once the process comes to a halt, you do not know what is happening around.
The human body, though of perishable nature, teaches one great lesson, namely, ‘Soham’ (That I am). When you inhale you make the sound ‘So’ and while exhaling you make the sound ‘Ham’. The process of inhalation represents life and that of exhalation, death. One moment is enough to attain freedom from life and life. You have to give up body attachment, which I am demonstrating right before you day in and day out... This body which I have taken upon Myself undergoes suffering. But I do not attach importance to the suffering. Many students and devotees have expressed anxiety and concern that might undergo a lot of suffering while the Linga emerges from My body. No doubt, your apprehensions are true but I do not feel any suffering. In fact, it is only when I identify Myself with the body, I undergo pain. Since I am not the body, I do not suffer any pain.
Some time back, when My hip bone got fractured, I was taken to the hospital. The doctors were planning to perform a major orthopaedic surgery. I told them, ‘You can do whatever you wish to. This body is yours. I am not the body. I am I’. The doctors performed a major operation on this body. But I did not suffer any pain. Whatever pain was there, only the body suffered, not Me. If you also adopt a similar attitude, you will not feel any pain. Therefore, reduce your Dehabhimana gradually. (SSS Vol.37, pp. 74-76)