Lord Krishna taught Arjun during the beginning of the war of Mahabharata about how Karma and life are intertwined. The most famous quotes said by him were:

“yada yada hi dharmasya
glanir bhavati bharata
abhyutthanam adharmasya
tadatmanam srjamy aham” (Bhagwat Gita: Chapter Four verse 7)

By this krishna meant to say that ” whenever and wherever there is a decline in the virtue/religious practice, O Arjuna and the rise of dominance of irreligion, then i descend on earth as an embodied being.”

“na jayate mriyate va kadacin
nayam bhutva bhavita va na bhuyah
ajo nityah sasvato ’yam purano
na hanyate hanyamane sarire” (Bhagwat Gita: Chapter Two verse 20)

Krishna says ” Soul was never born and neither it will die. It never came into being, does not comes into being and never would come into being. Soul is eternal, ever existing and primeval. it is not slain , killed or hurt when the body is harmed.”

“paritranaya sadhunam
vinasaya cha duskritam
sambhavami yuge yuge” (Bhagwat Gita: Chapter Four verse 8)

Krishna meant ” To annihilate the miscreants from the society, I take birth on earth to re-establish faith in goodness and the balance of life. I am reborn millennium after millennium to strive balance in society.”

“karmany evadhikaras te
ma phalesu kadachana
ma karma-phala-hetur bhur
ma te sango ’stv akarmani” (Bhagwat Gita: Chapter Two verse 47)

Krishna preached Arjun when Arjun had refused to fight his own kins: ” You have the right to perform your duties, but you are not entitled to bare the fruits of action. Never consider yourself as the cause of the results of your activities and never be attached to not doing your activity as well.”

“vasamsi jirnani yatha vihaya
navani grhnati naro ’parani
tatha sarirani vihaya jirnany
anyani samyati navani dehi” (Bhagwat Gita: Chapter Two verse 22)

Krishna said: ” As a person puts on new clothes and discards the old ones, similarly the soul gives up the physical being and moves onto the new one.”