Imam explains the matter through his famous work "the combat with the self" as following:
However, one who has not yet torn the veils of darkness, one who directs all of his attention to the natural world and, God forbid, becomes deviated from Allah, and one who is basically unaware of the world beyond and the spiritual worlds, and has retrogressed to a state of nature, who has never decided to refine himself, to set into motion his spiritual powers, to push aside the curtains of darkness which are a cloud over his heart.
He is lodged in ‘the deepest of the depths’ [of hell] which is the ultimate veil.
“Then we render him the lowest of the low” (95:5)
While the God of the worlds has created man in the most lofty state and station, Imam further explains.
“Indeed we have created man in the best of molds” (95:4)
If one follows the desires of the self and from the day he becomes acquainted with himself pays no attention to anything other than the dark wilderness and never thinks that it is possible that aside from this polluted dark world that there exists another place and station, then he will have sunk into the veil of darkness and have become an instance of,
“But he clung to the earth and followed his low desire” (7:176).
With such a heart polluted by sin that he has been covered by the curtain of darkness, and with such a gloomy spirit that due to the effect numerous sins he has become far from God, the Exalted, that worship of desire and seeking after the world have blinded the intellect and eyes of truth, then he cannot be released from the veils of darkness, let alone to tear the veils of light and detach himself from all but Allah.
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Imam Khomeini stressed need for acquisition of virtues and human nobilities
The strongest sort of belief he might have would be not to deny the position of the saints [awliya] of God, and not to consider as myths the worlds of the barzakh, the sirat, the resurrection, the accounting, the book, heaven, and hell.
Due to the effects of sins and the attachment of the heart to this world, one comes to gradually deny these truths, to deny the positions of the saints [awliya] of God, positions which are mentioned in not more than a few lines of prayers and intimate devotions.
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Man is the child of this physical world, Imam Khomeini explains