Basics of Bhagvat Gita

Bhagvat Gita is a divine conversation between the Supreme Soul (GOD) and the minute soul (Living Entity).
Arjuna the most elevated devotee and the most dear friend of Lord Sri Krishna , lost his composure when he saw his very close friends and relatives in the battlefield of Kurushetra.
He lost his composure and was distressed with the thought of killing the very people whom he adored. This situation pertains to everyone in the material world , where in at some point of time everyone has to face such situations.

Lord Sri Krishna , says in Bhagvat Gita that all the sorrows and happiness , we experience in this material world is due to misidentification of ourselves.

What is this misidentification ?

Identifying onself with the material body or the mind is described herein as misidentification.

SO if we are not this body or the mind then what are we ?

Bhagvat Gita says, we are spirit souls. Our existence is not material , but spiritual. Our true identity is spiritual.

How can I believe that we are not this body and we are spirit soul, I dont see the soul?
There are many things which we dont see , but we believe them by our intelligence, for example air.
Similarly if we observe carefully , we can see the diffrence , between a dead body and the living body is the absence of soul. When a dead body is seen , it has all the organs and every other part which is present in a living body , but the dead body does not move, this should be proof enough to identify a living force , which moves the body of a living person , which apparently is missing from the dead body, and that living force is the spirit soul, out true identity.
Consciousness spread all over the body is the sympton of the presence of the spirit soul.