In Chapter II, verses 16 to 28, Sri Krishna graciously describes the Immortal Atma and gives a soothing message to all those who grieve at death of the body.
The following are the verses.
16. The unreal has no being, the Real no non-being. These two facts the Truth-seers perceive.
17. Know That which pervades all this to be Indestructible. That Immutable none can destroy.
18. These bodies of the embodied Self, which is eternal, indestructible and immeasurable, are said to have an end. Therefore, fight, O Arjuna!
19. He who takes the Self to be the slayer and he who thinks He is slain, neither of them knows; He slays not nor is He slain.
20. That is not born, nor does It ever die; nor, having been, does It ever cease to be. That unborn, eternal, abiding, primeval being is not slain when the body is slain.
21. Whosoever knows Him to be indestructible, eternal, unborn and inexhaustible, how can That man slay, O Arjuna, or cause to be slain?
22. Just as a man casts off worn-out clothes and puts on new ones, so also the embodied Self casts off worn-out bodies and enters others that are new.
23. Weapons cut It not, fire burns It not, water wets It not, wind dries It not.
24. Invulnerable He is, not to be burnt, not to be drenched or dried. He is eternal, all-pervading, changeless, motionless, enduring.
25. This [Self] is said to be unmanifested, unthinkable and unchangeable. Therefore, knowing This to be such, thou shouldst not grieve.
26. But, even if thou thinkest of It as being constantly born and dying, even then, O mighty-armed, thou shouldst not grieve!
27. For to him who is born death is indeed certain, and to him who dies birth is certain. Therefore you should not grieve for the inevitable.
28. Beings are unmanifested in their beginning, manifested in their middle state, O Arjuna, and unmanifested again in their end! What is there to grieve about?
In verse 30, Sri Krishna tells Arjuna:
This, the Indweller in the body of everyone, is always Indestructible, O Arjuna! Therefore, thou shouldst not grieve for any creature.