Tat Tvam Asi: You are That
Everything in this world can be divided into two categories — perishable and non-perishable — that which goes through cycles of change and that which does not change at all. There is no third category! One category is that of truth and the other of falsehood. One category is of the sentient and the other of the non-sentient. So everything is sentient or non-sentient, true or false, perishable or non-perishable.

We become whatever we connect ourselves with. If we connect ourselves with the perishable, we become perishable. What is perishable? Whatever comes to an end, whatever changes and whatever has change as its basic essence is perishable. Can we change nature? No, we cannot do that. The intrinsic nature of things cannot be changed. You, in your core, are immortal and imperishable - this cannot change. It is extremely difficult, almost impossible. The perishable cannot become imperishable. And the imperishable cannot become perishable. You cannot make something eternal, if by its very nature it is transient. And whatever is immortal can never die.
Now the question is, where do you position yourself? In the category of the ‘imperishable’ or that of the ‘perishable’. Do you see yourself as one with the non-sentient or the sentient? If someone says, “I associate myself with the perishable, but I wish to be imperishable,” then there cannot be a greater fool than him. It is in the nature of matter, the body and the world to change.

There are three stages and three states in which you can be, or in which you are right now. And these are: dehoham, jivoham and shivoham. Dehoham means: ‘I’ am a body, ‘I’ am this body made of skin and bones and apart from it, I am nothing. If your understanding is that ‘I’ am only a body, then you will keep this body happy by feeding it properly and will savour all the flavours that your palate can relish; see all the good things with your eyes; listen to all the lilting tunes with your ears; experience all the lust you can. Doing anything and everything which can titillate your senses is the stage of dehoham. In this state, no spiritual prospects are sought, so involution is not possible. We can say that it is the lowest rung in the spiritual ladder and millions of people live and die in this very ignorant state; never going deep within the heart, never seeking the truth of the self and always thinking of the mortal body.

After dehoham, the second stage is jivoham. I am a jiva. What does jiva mean? Jiva means the individual self. Due to ignorance, jiva identifies itself with the body. But know this well that when the body dies, ‘you’ do not die. The one who is in dehoham bhava always says, “When the body dies, I also die.” But the fact is that even though death has happened to your body, ‘you’ do not die. The body dies, but you live on. During sleep there is a temporary death of the mind. The mind does not think or dream about anything in deep sleep. In the same way, ‘you’ experience temporary death when the body dies. The jiva regards each ‘body’ given to him as his own or as an expression of his ‘I-ness’, which is essentially foolish.

Jivoham is the state of those people who have some degree of interest in religious matters. They know that this journey will continue even after this body dies. Your journey was there before death and will continue after death. ‘I’ was there before death and ‘I’ will remain. Everything else will be left behind. So jivoham is the second stage. When this stage comes, the jiva starts contemplating: So who sired me in the first place? Paramatma is my source, and ‘I’ am his reflection. Then he starts worshipping. It is only in the Jivabhava that the worship of God really begins.

This third stage is shivoham. The realisation of the true self is shivoham. Only if you see yourself as separate from the mind, body, intellect and senses will you be able to experience the bhava: ‘I’ am Shivaroopa. It cannot happen only at the intellectual level. It has to be experienced, lived. Once we cut through the sheath of ignorance with gyana, once we step out of this falsehood, then all we are left with is the pure self. And this pure self is Shiva. The word ‘Shiva’ that I am using here is not synonymous with Shankar. The word ‘Shiva’ means anandaswaroopa, vyapakswaroopa, satyaswaroopa. ‘Shiva’ means one who is benevolent and aham means ‘I’. This ‘I’ is in no way different from the pure form of Shiva. So, who are ‘you’? Shankaracharya says, ‘shivoham, shivoham’. While sleeping, waking, walking, talking and eating — this idea, this thought, should never go away, that in fact, ‘I’ am not a body.  Satchidanandaswaroopa is my real essence. Except this, whatever I believe about this ‘I’ is patent falsehood. We have to liberate ourselves from this very falsehood, this very ignorance.
(Excerpted from Know Thyself which encapsulates the profound exposition of classic work of Advaita Vedanta ‘Atmashatkam’ by Adi Shankaracharya)