In other words...

In other words, to the extent that one’s heart is stained by the dross of sin, one is proportionately sealed off from the path of truth and deprived of understanding the Divine Signs and benefiting from His light and guidance. It should also be noted that perversion and the shutting of the heart are not exclusive to unbelievers and hypocrites.

Detailed Answer In the Qur`an, various terms have been used to refer to the incorrigibility of the hearts of the unbelievers, hypocrites, and the spiteful; among them khatm (sealed), tab‘ (sealed), sarf (turned away), qufl (locked), marad (ill), rayn (tainted), etc. Of course, the shutting of the heart and its corruption is not exclusive to unbelievers and hypocrites.

The heart of the human being—including the believer—is twisted and sealed and deprived of comprehending the Divine Signs in proportion as it is contaminated with the dross of sin. Thus, sealing the heart refers to the shutting of this conduit for receiving Divine knowledge and inspiration, and the means of this sealing can be inferred from the hadiths mentioned below. Zurarah has narrated that Imam Muhammad b.

‘Ali al-Baqir (a.s) as having said: “There is not a servant but that his heart contains a white slate. When he commits a sin, a black dot appears on it. Thereafter, if he repents, that black dot will disappear, but if he continues the sin, the blackness will expand, such that it will ultimately cover the entire whiteness. After the white slate has been entirely covered, the possessor of that heart will never return to good and virtue.

And this is the meaning of the word of God where He says: ‘No indeed! Rather their hearts have been sullied by what they have been earning.’ ”(6) and (7) There are certain factors that cause the accumulation of dross in the heart.

In the Noble Qur’an, the following issues are enumerated as accounting for the sealing of the heart: disbelief (8); heedlessness and continuous indifference (9); vow-breaking and brazen sinfulness (10); obstinacy and distorting of the Divine Word (11); self-wildness and acting against one’s knowledge (12): causing corruption, dishonouring family ties (13).

Thus, the veils that cover one’s heart and the obstacles that impede the function of the spiritual heart, hearing, and sight are the results of one’s own volitional conduct. The Divine seal is set by way of punishment and not gratuitously.