Imam Khomeini explains the matter and sheds light on the subject through his famous book "an exposition on Forty Hadith" as following:
the spring of youth fades out and the autumn of his life sets in, his heart has no more a zest for mirth and joy, his organs lose their vitality and those activities lose their relish. His eyes dim, his hearing is impaired, his sense of touch and other senses and faculties weaken. Ability to get pleasure declines or is completely lost.
Then hosts of ailments make him an easy prey. His digestive, assimilative and excretory system fails, and his respiratory system cannot perform it: function properly.
Nothing but deep sighs, displeasure, regret and remorse are left to accompany him.
Thus, the duration of our exploitation of these bodily powers, from the days when one gains consciousness of good and bad till the process of decline sets in, is not more than thirty or forty years, even for a person of very strong constitution.
That too, if one does not happen to come across all sorts of diseases and afflictions, which we witness every day and forget about. If, for the time being, we take it for granted (although it has no reality), that a man can attain the age of one hundred and fifty years, with all opportunities of involving oneself fully in all the three indulgences-sensuality, passion and imagination, excluding all the chances of coming across any adversities and misfortunes, even this period of time would prove short, and pass soon like the winds and what would be in store for you for the next world? What benefit will you derive from all these treasures of amusements for your eternal life? What will save you from the horrors of the day of doom, helplessness, desolation and loneliness? What will you present on the Day of Judgment, and how would you face God, His angels, and His chosen servants and prophets?
Of course, nothing will accompany you except your wicked and sinful deeds, which will metamorphose you in such a form that would not be known to anybody except God.
Everything that you have heard and conceived about the infernal fire, torments of the grave and agonies of the Doomsday, etc., you measured them with the worldly fire and worldly pains. What a gross error you committed.
Fire of this world is relatively an accident, and all the horrors are easy to bear.
Your estimation of the other world on the basis of this one is imperfect and faulty. Even if the fire burning throughout the world is accumulated at one place, it will not be hot enough to burn the human soul.
In the next world, besides burning and roasting the body it will burn the soul and incinerate the heart also.