People with the knowledge of self (Ātmagnānam) do not grieve. Ātma agnānam is the cause of the grievance (samsāra).

Ātma agnānam is cause of Samsāra (grievance) and Ātmagnānam is the cause of Moksha (freedom from Samsāra, bondage, pain and fear). It is not freedom physically, but getting the strength and ability with knowledge to overcome these mentally.

Every human being has a fundamental problem of Samsāra. He is always in the sorrow of some or the other problem in his life.

Tatvārta - Bhagavān Krishna first addresses the fundamental problem of Arjuna and helps him understand himself (Ātmagyanam)

Dhārmika - Bhagavān then gives the Dhārmika reasons to fight the war.

Worldy reasons - Lastly he tells him that he needs to fight the war for the sake of his Name, fame and Status in the society

Consciousness is a independent principle, it is not a part, product or property of any 'body'. It always exists, irrespective of the existence of body or not.

Consciousness is a principle which pervades the entire body and is the reason of the functioning of the senses of the body

Consciousness is not bounded by any body, it exists without the body and also continues after the body has gone.

The presence of consciousness is not felt when the body is gone because the medium through which it is manifested is destroyed, but it continues to exist as an independent principle.

Every individual is a mixture of both Ātma and Anātma. The separate entities like - body, mind are all anātma, but an individual is said to be alive when he functions with senses thus existence of ātma.

Once we understand the principle of Consciousness we will start to live happily by accepting all the drawbacks and limitations of the body, we will start to live happily in spite of all the troubles and thus enjoy this life.