Wisdom from the Bhagavad Gita 3

10. To him who was sorrowing in the midst of the two armies, Hrishikesha, as if smiling, O descendant of Bharata! spoke these words. 

The Blessed Lord said: 

11. You have been mourning for them who should not be mourned for. Yet you speak words of wisdom. The truly wise grieve neither for the living nor the dead. 

12. It is not that I have never existed, nor you, nor these kings. Nor is it that we shall cease to exist in the future.

13. As are childhood, youth, and old age, in this body, to the embodied soul, so also is the attaining of another body. Calm souls are not deluded by this.

14. Notions of heat and cold, of pain and pleasure, are born, O son of Kunti, only of the contact of the senses with their objects. They have a beginning and an end. They are impermanent in their nature. Bear them patiently, O descendant of Bharata.

15. That calm man who is the same in pain and pleasure, whom these cannot disturb, alone is able, O great among men, to attain to immortality.

16. The unreal never is. The Real never is not. Men possessed of the knowledge of the Truth fully know both these.

17. That by which all this is pervaded—That know for certain to be indestructible. None has the power to destroy this Immutable.

18. Of this indwelling Self, the ever-changeless, the indestructible, the illimitable—these bodies are said to have an end. Fight therefore, O descendant of Bharata.

—Bhagavad Gita, 2:10-18