Imam Khomeini explains the matter through his theological works as following:
From the manners of some and their way of living it is obvious that they do not even consider the existence of a supernatural world to be possible, since the mere consideration of this possibility keeps man from committing many wrongs.
Is it possible for someone to consider it possible that hell exists and that one may remain forever in its fire while at the same time doing wrong?
Can it be said that one who considers God Almighty to be present and watching and Who sees himself to be in the presence of the Lord, and who considers it possible that there should be retribution for his words and deeds, a reckoning and chastisement, and that in this world every word he speaks, every step he takes, every deed he does, is recorded by angels of Allah called ‘Raqib and ‘Atid,’ and they carefully record all his words and deeds, and in such a state, could he fearless of his own doing?
It is painful [to realize] that they do not even consider these truths to be possible.