In the Name of Allah, the Most Gracious, the Most Merciful.
The Qur'an is Guidance and Glad Tidings for the Believers, a Warning to the Disbelievers, and it is from Allah
In (the comments on) Surat Al-Baqarah, we discussed the letters which appear at the beginning of some Surahs.
تِلْكَ ءَايَـتُ الْقُرْءَانِ وَكِتَـبٍ مُّبِينٍ
(These are the Ayat of the Qur'an, and (it is) a Book (that is) clear.) It is plain and evident.
هُدًى وَبُشْرَى لِلْمُؤْمِنِينَ
(A guide and glad tidings for the believers.) meaning, guidance and good news may be attained from the Qur'an for those who believe in it, follow it and put it into practice. They establish obligatory prayers, pay Zakah and believe with certain faith in the Hereafter, the resurrection after death, reward and punishment for all deeds, good and bad, and Paradise and Hell. This is like the Ayat:
زَيَّنَّا لَهُمْ أَعْمَالَهُمْ (We have made their deeds adorned in their sight - 27:4)It means that those who do not believe in the Hereafter We have made their bad actions look adorned in their sight. Therefore they feel good about them and remain enthralled in depravity. Some commentators have interpreted that "their deeds" is used in this verse for good deeds. Hence meaning of the verse is that Allah had placed the good deeds before them with all their attractions. But those unjust people did not pay any attention to them, rather they remained engrossed in infidelity; hence lost their way in wilderness.
However, the first interpretation looks more appropriate and straightforward. In the first place, in the Qur'an, the word (Zinah) 'adornment' has been generally used for bad actions, for instance: زُيِّنَ لِلنَّاسِ حُبُّ الشَّهَوَاتِ (It has been made attractive for people to love the desires - 3:14) زُيِّنَ لِلَّذِينَ كَفَرُوا الْحَيَاةُ الدُّنْيَا (Adorned is the present life for those who disbelieve - 2:212) زَيَّنَ لِكَثِيرٍ مِّنَ الْمُشْرِكِينَ (6:137). Its use for good actions is very rare , such as: وَلَـٰكِنَّ اللَّـهَ حَبَّبَ إِلَيْكُمُ الْإِيمَانَ وَزَيَّنَهُ فِي قُلُوبِكُمْ (But Allah has endeared to you belief, decking it fair in your hearts - 49:7). Secondly, the word اَعمَالَھُم (their deeds) used in the verse is also pointing out that bad actions are meant here and not the righteous actions.
Tazkirul Quran
Maulana Wahiduddin KhanOn ayahs 6–7
When Truth appears before a man and he accepts it without any reservation, he immediately finds himself on the right path. His life becomes righteous in every respect. But, one who is not prepared to mould himself in accordance with the Truth, is forced to twist reality to suit himself. From this develops an attitude of perverseness which is expressed here as ‘their actions appear beautiful to them’ (zayyanna lahum a‘malahum). One with such an attitude seeks self-made arguments to justify his behaviour. These so-called arguments gradually take hold of his mind in such a way that he believes them to be perfectly correct. In the light of his false reasoning, his misdeeds appear virtuous to him. Those to whom God has made their misdeeds appear beautiful are those who are not serious about the call to accept the Truth. As a result of this thinking, they become completely unmindful of self-reformation. They have to pay a heavy price for this tendency of theirs to consider their wrong as right: the path they tread leads straight to hell.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.