Tafseer of The Cave · Al-Kahf · 18:2
[He has made it] straight, to warn of severe punishment from Him and to give good tidings to the believers who do righteous deeds that they will have a good reward
Important: The Arabic source text is always authoritative. This translation is a study aid and has not been verified by scholars — do not use it as a basis for religious proof or for deriving rulings (ahkam). When in doubt, always consult the Arabic text and a qualified scholar.
The explanation of the words of Allah the Exalted: قَيِّمًا لِيُنْذِرَ بَأْسًا شَدِيدًا مِنْ لَدُنْهُ وَيُبَشِّرَ الْمُؤْمِنِينَ الَّذِينَ يَعْمَلُونَ الصَّالِحَاتِ أَنَّ لَهُمْ أَجْرًا حَسَنًا (upright, that he may warn of a severe punishment from Him, and that he may bring the believers who perform good works the good news that they shall have an excellent reward — verse 2)
Allah the Exalted says: He has sent down upon His servant the Qurʾān in an upright, straight condition, with no crookedness in it, that He may warn you, O people, of a severe punishment (baʾs) from Allah. By the baʾs He means the imminent torment, the present punishment, and the act of might. His words مِنْ لَدُنْهُ mean: from Allah Himself.
And in accordance with the purport of what we have said about this, the exegetes have spoken.
* Mention of who said this:
Abū Kurayb related to us, saying: Yūnus ibn Bukayr related to us, on the authority of Muḥammad ibn Isḥāq, concerning لِيُنْذِرَ بَأْسًا شَدِيدًا (that he may warn of a severe punishment): "a punishment that is already executed with haste in this world, and a torment in the Hereafter." مِنْ لَدُنْهُ : that is, from your Lord who has sent you as a messenger.
Ibn Ḥumayd related to us, saying: Salama related to us, on the authority of Ibn Isḥāq, to the same effect.
Bishr related to us, saying: Yazīd related to us, saying: Saʿīd related to us, on the authority of Qatāda, concerning his words مِنْ لَدُنْهُ : that is, from Him.
As for the question: where is the object of the verb لِيُنْذِرَ — the object has been omitted, but the sentence is sufficient indication of it; it is implicitly present, connected with yundhira before the word baʾs, as though it said: that he may warn you of a punishment — just as it is also said: يُخَوِّفُ أَوْلِيَاءَهُ [Āl ʿImrān: 175], which means: he frightens you with his friends.
His words وَيُبَشِّرَ الْمُؤْمِنِينَ mean: and that he may bring the good tidings to the believers in Allah and His Messenger, الَّذِينَ يَعْمَلُونَ الصَّالِحَاتِ — that is, acting according to what Allah has commanded be done, and abstaining from what Allah has forbidden — أَنَّ لَهُمْ أَجْرًا حَسَنًا — that is: an abundant reward for them with Allah on account of their faith in Allah and His Messenger, and on account of their good works in this world. That reward is the Paradise (janna) that has been promised to the pious.