The Christians would say that the purpose of life is to serve God and suffer for one decade after the next, attempting to survive until such time as you are no longer able and God, in his unknowable wisdom, kills your ass dead in order to reward you in Heaven.
The athiests would say that you must eat, fight, and breed in order to propogate your genetics.
The spiritualists would say it is to find internal peace and happiness.
The humanitarians would say it is to serve man in order to better the quality of life.
I believe it is to leave the world a better place than how you found it.