From the Bhagavad Gita:

When the senses contact sense objects, a

person experiences cold or heat, pleasure or

pain. These experiences are fleeting; they

come and go. Bear them patiently, Arjuna.

Those who are not affected by these changes, 

who re the same in pleasure and pain, are

truly wise and fit for  immortality. Assert your

strength and realize this!

The impermanent has no reality; reality

lies in the eternal. Those who have seen the

boundary between these two have attained the

end of all knowledge. Realize that which

pervades the universe and is indestructible; no

power can affect this unchanging, imperishable

reality. The body is mortal, but he who

dwells in the body is immortal and immeasurable.

Therefore, Arjuna, fight in this battle.