What destroys the highest inherent capabilities of Qalb
عَنْ أَبِى هُرَيْرَةَ أَنَّ رَسُولَ اللَّهِ -صلى الله عليه وسلم- قَالَ : إِنَّ الْمُؤْمِنَ إِذَا أَذْنَبَ كَانَتْ نُكْتَةٌ سَوْدَاءُ فِى قَلْبِهِ فَإِنْ تَابَ وَنَزَعَ وَاسْتَغْفَرَ صُقِلَ قَلْبُهُ فَإِنْ زَادَ زَادَتْ فَذَلِكَ الرَّانُ الَّذِى ذَكَرَهُ اللَّهُ فِى كِتَابِهِ ( كَلاَّ بَلْ رَانَ عَلَى قُلُوبِهِمْ مَا كَانُوا يَكْسِبُونَ)
Abu Huriarah (RA) narrates that Rasulullah (Sallallahu Alaihi Wasallam) has said: "Indeed when a man commits sin, there occurs a black stain on his heart. Then if he repents and asks forgiveness (from Allah Ta’ala) his heart gets cleaned and if he commits more sins, that black stain increases in size till it covers the whole heart. It is that cover of impure (sins), which has been called Ra'an (rust), which Allah Ta’ala mentions in the verse No. (83:14)” (Ibn Majah)
كَلَّا بَلْ رَانَ عَلَى قُلُوبِهِمْ مَا كَانُوا يَكْسِبُونَ
"By no means! But on their hearts is the stain of the (ill) which they do”. (83:14)
The heart of man, as created by Allah Ta’ala is pure and unsullied. When a man does an evil deed, it makes a stain on his heart. But on repentance or forgiveness, this stain gets washed off. If such a person doesn't repent or is not forgiven, this stain deepens as well as spreads more and more, until his heart is sealed and eventually he dies a spiritual death. These are such stains which prevent the heart from perceiving truths which are otherwise obvious to enlightened hearts.
Allah Ta’ala says
خَتَمَ اللَّهُ عَلَى قُلُوبِهِمْ وَعَلَى سَمْعِهِمْ وَعَلَى أَبْصَارِهِمْ غِشَاوَةٌ وَلَهُمْ عَذَابٌ عَظِيمٌ
“AlIah hath set a seal on their hearts and on their hearing and on their eyes is a veil, Great is the chastisement They (incur). (2: 7)
Pure heart is like a mirror. If it is free from these evil stains, it has the ability to receive and reflect the Divine Light which penetrates the veils lying between the Reality and the eyes. But if this mirror of Qalb (Divine) is stained with evil deeds, it gets sullied and hence unable to receive this light. It loses its function and becomes as good as dead. This dead state of Qalb is here referred to in Aayat (2:7) as a seal, as if their hearts have been sealed.
The biggest and the darkest stain on Qalb is caused by Kufr (not believing in Allah Ta’ala and His Messenger—Rasulullah (Sallallahu Alaihi Wasallam) )
This evil almost completely darkens the Qalb and one can say it gets completely sealed or shut off from the Reality.
In case of believers the ratio of the stain on Qalb and the evil deeds is directly proportional. More the evil deeds, more the stains and vice versa. If a believers do not desist from these kind of deeds and remains adamant on the evil deeds of major significance, there is every apprehension that his heart may also get sealed which he may not be even knowing.
May Allah Ta’ala protect our hearts from this disease- Aamin.
Allah Ta’ala says in the Qur’ân:
فَبِمَا نَقْضِهِمْ مِيثَاقَهُمْ وَكُفْرِهِمْ بِآيَاتِ اللَّهِ وَقَتْلِهِمُ الْأَنْبِيَاءَ بِغَيْرِ حَقٍّ وَقَوْلِهِمْ قُلُوبُنَا غُلْفٌ بَلْ طَبَعَ اللَّهُ عَلَيْهَا بِكُفْرِهِمْ فَلَا يُؤْمِنُونَ إِلَّا قَلِيلًا
“(They have incurred divine displeasure): In that they broke their covenant. That they rejected the signs of Allah Ta’ala; that they slew the Messenger in defiance of right; that they said, “ Our hearts are the wrappings” Nay, Allah Ta’ala hath set the seal on their hearts for their blasphemy, And little is it they believe”.(4:155)
أَفَلَا يَتَدَبَّرُونَ الْقُرْآنَ أَمْ عَلَى قُلُوبٍ أَقْفَالُهَا
"Do they not then Earnestly seek to understand The Qur’ân, or is that there are Locks upon their Hearts.” (47:24)
Because of these serious evils, Allah Ta’ala sets the seal on their hearts so that they no more deserve the Divine Light and divine pleasure. Rasulullah (Sallallahu Alaihi Wasallam) , says that: "The hardened heart (the heart which is stained and darkened) is disliked by Allah Ta’ala the most.”.