Imam Khomeini in his famous book on "Discipline of prayers" explains the matter as following:
It is one of the important stages for the sālik (traveler).
The strength of everybody's sulūk (journey) is in proportion to the strength of this attention, or rather the perfection or the imperfection of humanity is connected to the perfection or imperfection of this matter.
The more one is overwhelmed by egoism, egotism, self-conceit and selfishness, the farther he will be from the human perfection and from the nearness of the presence of Allah.
The veil of self-conceit and egotism is thicker and darker than all other veils. To tear open this veil is more difficult than tearing all other veils, and tearing it is a preparatory step to tearing other veils.
In fact, tearing off this veil is the master key for the invisible, the visible and the great door of the ascent to the perfect spirituality.
As long as man has his eyes on his own self, his imagined beauty and perfection, he will be veiled and discarded from the absolute beauty and pure perfection.
The first condition for traveling to Allah is to leave this house. Actually, it is the criterion for the struggle between right and wrong.
So, every sālik, who travels with the steps of selfishness and self-conceit, and is wrapped in the veils of egotism, his sufferings would be in vain and his journey would not be to Allah, it would rather be to his self: “The mother of the idols is the idol of your self.”
Allah, the Most High, says:
“And whoever leaves his house migrating to Allah and His Messenger, and then death overtakes him, his reward is, indeed, with Allah.”