In plain words
This is what they called “Svavimarśo mokṣaḥ”: enquiry into oneself is liberation. In this world, when every person introduces himself, each one uses the word ‘I, I’, saying ‘I am Rāma’, ‘I am Sītā’, and speaks about himself. So, though there are many differences, the word ‘I’ runs through all human beings like the thread through the beads. So every person must grasp that it is essential to understand this principle called “I” well.
What is ‘I’?
Because man mistakes this impermanent body for ‘I’, he becomes subject to many sorrows. “Aham etat na”: so the Śruti teaches the knowledge of one’s true nature. Aham means I, etat means this, na means not. That is, ‘I am not this.’ That is the meaning. This very knowledge brings to mind one’s nature as Sat, Cit and Ānanda, and awakens right knowledge. What is ‘I’? On the authority of the Śruti it is known that the word “I” has many names: Ātma, Paramātma, Brahman, Pratyagātma. In every human being this ‘I’ takes the form of Vaiśvānara, digesting the food that is eaten and spreading its essence through every limb. For this reason the ‘I’ dwells in every human being in the form of Vaiśvānara. Paramātma, it must be said, means the principle that is beyond the organs of action, the organs of knowing, the Manas and Buddhi, the citta and Ahaṅkāra. This principle of the Paramātma has come to be given form as the principle of Brahman.
‘I’ am not the body
What is Brahman? To pervade everything is the principle of Brahman. In every human being the “I” pervades. So the “I” that pervades all human beings is called “Brahman”. The ‘I’ is the very form of Brahman. Then the word ‘this’ pervades every object that is seen. For example, we say: this is a mike, this is the sun, this is the moon. So the word ‘this’ lies hidden within the things that are seen. In short, we must grasp its inner meaning: the word ‘this’ belongs to the things that are seen. Without the word ‘this’, when one speaks of a cloth, the question comes, ‘Which cloth?’ Then it is pointed out by saying, “This is the cloth.” So it is the principle that pervades all seen things that bears the name “this”. ‘This’ is the seen; ‘I’ is the seer. So the “I” is not the seen; what the “I” wears is “this”, and that is the body. Just as I see everything, I see my body. The body too is something seen.