Imam Khomeini explains the matter in his famous book of “an exposition on Forty Hadith” as following:
Let it be known to you that this world, due to its defective, feeble and weak nature, is neither the abode of the reward of God Almighty nor the place of His chastisement and punishment.
This is so because the abode of Divine munificence is a realm whose bounties are pure, unadulterated with torment, and its comforts are not mixed with pain and grief.
Such bounties are not possible in this world, which is an abode where contradictories throng together and each of whose bounties is mixed with numerous kinds of pains, hardships and torments.
Rather, as the philosophers have said, pleasure in this world lies in avoiding pain. It may be said that even its pleasures cause pain and every one of its pleasures is followed by pain and hardship.
Rather, the very material of this world lacks the capacity to accept absolute goodness and unadulterated bounty.
In the same way, its pains and hardships, torments and punishments are also mixed; each of its pains and hardships carries within itself some goodness and bounty, and none of its afflictions and adversities is unmixed.
The very material of this world lacks the capacity to accept pure, absolute punishment, whereas the abode of Divine chastisement is a place where punishment is pure and absolute; its pains and afflictions are not like those of this world, which while they afflict one member of the body are absent from the other members.
While the healthy members are in comfort and ease, the afflicted member suffers pain and agony.