If a person is not engaged in Krsna consciousness and devotional service, it is useless for him to exhibit the symptoms of life. Generally if a person is breathing he is accepted to be alive. But a person without Krsna consciousness may be compared to a bellows in a blacksmith’s shop. The big bellows is a bag of skin which exhales and inhales air, and a human being who simply lives within the bag of skin and bones without taking to Krsna consciousness and loving devotional service is no better than the bellows. Similarly, a nondevotee’s long duration of life is compared to the long existence of a tree, his voracious eating capacity is compared to the eating of dogs and hogs, and his enjoyment in sex life is compared to that of hogs and goats.

If a human being does not fulfill the mission of his life by worshiping the Supreme Lord and does not go back home, back to Godhead, it is to be understood that he is breathing just like a blacksmith’s bellows, living just like a tree, eating just like a camel and having sex just like the dogs and hogs. Thus he has been frustrated in fulfilling the specific purpose of human life.

From Krsna Book chapter 87, by Srila Prabhupada