Commanding the people to reflect and ponder upon the Qur'an, and prohibiting them from turning away from it, Allah says,
أَفَلاَ يَتَدَبَّرُونَ الْقُرْءَانَ أَمْ عَلَى قُلُوبٍ أَقْفَالُهَآ
(Will they not then reflect upon the Qur'an, or are there locks upon their hearts) means, there indeed are locks upon some hearts, firmly closing them so that none of its meanings can reach them. Ibn Jarir recorded from Hisham bin `Urwah, from his father, may Allah be pleased with him, that Allah's Messenger ﷺ once recited this Ayah,
أَفَلاَ يَتَدَبَّرُونَ الْقُرْءَانَ أَمْ عَلَى قُلُوبٍ أَقْفَالُهَآ
(Will they not then reflect upon the Qur'an, or are there locks upon their hearts) and a young man from Yemen said, "Indeed, there are locks upon them -- until Allah opens them totally or slightly." After that `Umar, may Allah be pleased with him, always liked that young man, and kept that to himself until he became in charge, upon which he utilized him (as a consultant).
Allah then says,
إِنَّ الَّذِينَ ارْتَدُّواْ عَلَى أَدْبَـرِهِمْ
(Verily, those who have turned back) meaning, they departed from the faith and returned to disbelief.
مِّن بَعْدِ مَا تَبَيَّنَ لَهُمُ الْهُدَى الشَّيْطَـنُ سَوَّلَ لَهُمْ
(... after guidance had become clear to them -- Shaytan has enticed them) meaning he adorned and beautified that (apostasy) for them.
وَأَمْلَى لَهُمْ
(and filled them with false hopes.) meaning, he tempted them, and deceived them.
ذَلِكَ بِأَنَّهُمْ قَالُواْ لِلَّذِينَ كَرِهُواْ مَا نَزَّلَ اللَّهُ سَنُطِيعُكُمْ فِى بَعْضِ الاٌّمْرِ
(That is because they said to those who hate what Allah sent down: "We will obey you in part of the matter.") means, they plotted secretly with them and gave them evil advice -- as is the common practice of the hypocrites who declare the opposite of what they conceal. Because of this, Allah says,
وَاللَّهُ يَعْلَمُ إِسْرَارَهُمْ
(And Allah knows their secrets. ) whatever they hide and conceal, Allah is well-acquainted with it and He knows it. This is similar to His saying,
وَاللَّهُ يَكْتُبُ مَا يُبَيِّتُونَ
(...And Allah records all that they plot by night.) (4:81) Allah then says,
فَكَيْفَ إِذَا تَوَفَّتْهُمُ الْمَلَـئِكَةُ يَضْرِبُونَ وُجُوهَهُمْ وَأَدْبَـرَهُمْ
(How (will it be) when the angels will take their souls at death, striking their faces and their backs) That is, how their situation will be when the angels come to take their lives, and their souls cling to their bodies, causing the angels to extract them by force, harshness, and beating. This is similar to Allah's saying,
وَلَوْ تَرَى إِذْ يَتَوَفَّى الَّذِينَ كَفَرُواْ الْمَلَـئِكَةُ يَضْرِبُونَ وُجُوهَهُمْ وَأَدْبَـرَهُمْ
(If you could but see when the angels take away the lives of the disbelievers, striking their faces and their backs.) (8:50) And His saying,
وَلَوْ تَرَى إِذِ الظَّـلِمُونَ فِى غَمَرَاتِ الْمَوْتِ وَالْمَلَـئِكَةُ بَاسِطُواْ أَيْدِيهِمْ
(If you could but see when the wrongdoers are in the agonies of death, while the angels extend their hands) (6:93). meaning, to beat them.
أَخْرِجُواْ أَنفُسَكُمُ الْيَوْمَ تُجْزَوْنَ عَذَابَ الْهُونِ بِمَا كُنتُمْ تَقُولُونَ عَلَى اللَّهِ غَيْرَ الْحَقِّ وَكُنتُمْ عَنْ ءَايَـتِهِ تَسْتَكْبِرُونَ
((saying): "Deliver your souls! This day you will be recompensed with the torment of degradation because of what you used to utter against Allah other than the truth, and because you used to arrogantly reject His signs.") (6:93) Because of the above, Allah says,
ذَلِكَ بِأَنَّهُمُ اتَّبَعُواْ مَآ أَسْخَطَ اللَّهَ وَكَرِهُواْ رِضْوَانَهُ فَأَحْبَطَ أَعْمَـلَهُمْ
(That is because they pursued what angered Allah and disliked what earns His pleasure, so He rendered their deeds worthless.)