आत्मा

In the Gita, ātman does not mean a small object hidden somewhere inside the body. It is the name for the knower who stays one through all our changes: from childhood to old age, from joy to sorrow, and even from one body to another.

In the second chapter Lord Krishna gives several marks of it. It is never born and never dies (2.20). That by which all this is pervaded is imperishable (2.17). Weapons do not cut it, fire does not burn it, water does not wet it, wind does not dry it (2.23). It is called unmanifest, inconceivable and unchanging (2.25). All of these tell us what class of thing it is not: it is not like the body, something that a blade could reach.

For that reason the Gita points toward seeing it rather than defining it. What changes is called the body; what watches the change and remains is the self.

This does not mean the body is trivial, or that sorrow is a sin. Knowing the self does not take the pain away, but it gives pain a ground beneath it that does not break.