As-Suddi said that,

﴿خَتَمَ اللَّهُ﴾

(Khatama Allah) means, "Allah has sealed.'' Qatadah said that this Ayah means, "Shaytan controlled them when they obeyed him. Therefore, Allah sealed their hearts, hearing and sight, and they could neither see the guidance nor hear, comprehend or understand.'' Ibn Jurayj said that Mujahid said,

﴿خَتَمَ اللَّهُ عَلَى قُلُوبِهِمْ﴾

(Allah has set a seal on their hearts), "A stamp. It occurs when sin resides in the heart and surrounds it from all sides, and this submersion of the heart in sin constitutes a stamp, meaning a seal.'' Ibn Jurayj also said that the seal is placed on the heart and the hearing. In addition, Ibn Jurayj said, that `Abdullah bin Kathir narrated that Mujahid said, "The stain is not as bad as the stamp, the stamp is not as bad as the lock which is the worst type.'' Al-A`mash said, "Mujahid demonstrated with his hand while saying, `They used to say that the heart is just like this - meaning the open palm. When the servant commits a sin, a part of the heart will be rolled up - and he rolled up his index finger. When the servant commits another sin, a part of the heart will be rolled up' - and he rolled up another finger, until he rolled up all of his fingers. Then he said, `Then, the heart will be sealed.' Mujahid also said that this is the description of the Ran (refer to 83:14).''

Al-Qurtubi said, "The Ummah has agreed that Allah has described Himself with sealing and closing the hearts of the disbelievers, as a punishment for their disbelief. Similarly, Allah said,

﴿بَلْ طَبَعَ اللَّهُ عَلَيْهَا بِكُفْرِهِمْ﴾

(Nay, Allah has set a seal upon their hearts because of their disbelief) (4:155).''

He then mentioned the Hadith about changing the hearts, (in which the Prophet supplicated),

«يَا مُقَلِبَ الْقُلُوبِ ثَبِّتْ قُلُوبَنَا عَلى دِينِك»

(O You Who changes the hearts, make our hearts firm on Your religion.)

He also mentioned the Hadith by Hudhayfah recorded in the Sahih, in which the Messenger of Allah said,

«تُعْرَضُ الْفِتَنُ عَلَى الْقُلُوبِ كَالْحَصِيرِ عُودًا عُودًا، فَأَيُّ قَلْبٍ أُشْرِبَهَا نُكِتَ فِيه نُكْتَةٌ سَوْدَاءُ وَأَيُّ قَلْبٍ أَنْكَرَهَا نُكِتَ فِيهِ نُكْتَةٌ بَيْضَاءُ حَتى تَصِيرَ عَلَى قَلْبَيْنِ: عَلى أَبْيَضَ مِثْلِ الصَّفَا، فَلَا تَضُرُّهُ فِتْنَةٌ مَا دَامَتِ السَّمَوَاتُ وَالْأَرْضُ وَالْآخَرُ أَسْوَدُ مُرْبَادًّا كَالْكُوزِ مُجَخِّيًا لَا يَعْرِفُ مَعْرُوفًا وَلَا يُنْكِرُ مُنْكَرًا»

(The Fitan (trials, tests) are offered to the hearts, just as the straws that are sewn into a woven mat, one after another. Any heart that accepts the Fitan, then a black dot will be engraved on it. Any heart that rejects the Fitan, then a white dot will be engraved on it. The hearts will therefore become two categories: white, just like the barren rock; no Fitnah shall ever harm this category as long as the heavens and earth still exist. Another category is black, just as the cup that is turned upside down, for this heart does not recognize righteousness or renounce evil. )

Ibn Jarir said, "The truth regarding this subject is what the authentic Hadith from the Messenger of Allah stated. Abu Hurayrah narrated that the Messenger of Allah said,

«إِنَّ الْمُؤمِنَ إِذَا أَذْنَبَ ذَنْبًا كَانَتْ نُكْتَةً سَوْدَاءَ فِي قَلْبِهِ، فَإِنْ تَابَ وَنَزَعَ وَاسْتَعْتَبَ صَقِلَ قَلْبُهُ وَإِنْ زَادَ زَادَتْ حَتَّى تَعْلُوَ قَلْبَهُ، فَذلِكَ الرَّانُ الَّذِي قَالَ اللهُ تَعَالى:

﴿كَلاَّ بَلْ رَانَ عَلَى قُلُوبِهِمْ مَّا كَانُواْ يَكْسِبُونَ ﴾

(When the believer commits a sin, a black dot will be engraved on his heart. If he repents, refrains and regrets, his heart will be polished again. If he commits more errors, the dots will increase until they cover his heart. This is the Ran (stain) that Allah described,

﴿كَلاَّ بَلْ رَانَ عَلَى قُلُوبِهِمْ مَّا كَانُواْ يَكْسِبُونَ ﴾

(Nay! But on their hearts is the Ran (stain) which they used to earn)'' (83:14).

At-Tirmidhi, An-Nasa'i and Ibn Majah recorded this Hadith, and At-Tirmidhi said that it is Hasan Sahih.