Preaching on the immortality of the soul

Arjuna's dilemma and guidance of Sri Krishna

In the second chapter of the Bhagavad Gita, Arjuna is mourning the moral dilemma of fighting against his own kinsmen on the battlefield of Kurukshetra. He says to Sri Krishna, "O Govinda, I will not fight," and falls silent. In this mourning state, Sri Krishna smilingly preaches to him on the immortality of the soul.
He says that Arjuna is mourning for those for whom mourning is inappropriate, because wise people mourn neither for the living nor for the dead. Sri Krishna clarifies that the soul is eternal, infinite and indestructible, which is never born and never dies. Death is only a change of the body, not of the soul. This preaching is meant to remove Arjuna's fear and grief and guide him on the path of duty.
Example: Suppose, a person is mourning the death of a loved one. This preaching of the Gita makes him understand that the loved one whom he thinks is lost is eternal as the soul. Just as a person's existence does not end by changing clothes, similarly the soul is not destroyed by changing the body. By understanding this truth, a person can be free from grief and can perform his duties, like Arjun had to follow his dharma in the war.