The Punishment of the Disbeliever and the Reward of the Believer on the Day of Resurrection
Having stated that the ultimate destiny of the followers of Iblis will be the blazing Fire, Allah then tells us that for those who disbelieve there will be a severe punishment. This is because they obeyed the Shaytan and disobeyed Ar-Rahman. And He tells us that those who believed in Allah and His Messengers
وَعَمِلُواْ الصَّـلِحَـتِ لَهُم مَّغْفِرَةٌ
(and do righteous good deeds, theirs will be forgiveness) meaning, from whatever sins they did,
وَأَجْرٌ كَبِيرٌ
and a great reward. for the good deeds that they did. Then Allah says:
أَفَمَن زُيِّنَ لَهُ سُوءَ عَمَلِهِ فَرَءَاهُ حَسَناً
(Is he, then, to whom the evil of his deeds is made fairseeming, so that he considers it as good) meaning, `such as disbelievers or immoral persons who do evil deeds and believe that they are doing something good, i.e., a person who is like that has been misguided by Allah, so what can you do for him You cannot help him at all.'
فَإِنَّ اللَّهَ يُضِلُّ مَن يَشَآءُ وَيَهْدِى مَن يَشَآءُ
(Verily, Allah sends astray whom He wills and guides whom He wills.) means according to His decree.
فَلاَ تَذْهَبْ نَفْسُكَ عَلَيْهِمْ حَسَرَتٍ
(So destroy not yourself in sorrow for them. ) means, do not grieve about that, for Allah is Wise in His decree and He leaves astray whomsoever He leaves astray, and He guides whomsoever He guides, and in doing so He has perfect knowledge and wisdom. Allah says:
إِنَّ اللَّهَ عَلِيمٌ بِمَا يَصْنَعُونَ
(Truly, Allah is the All-Knower of what they do!)
Tafsir Ibn Kathir (abridged, English).