فَمَنْ يُرِدِ اللَّهُ أَنْ يَهْدِيَهُ يَشْرَحْ صَدْرَهُ لِلْإِسْلَامِ وَمَنْ يُرِدْ أَنْ يُضِلَّهُ يَجْعَلْ صَدْرَهُ ضَيِّقًا حَرَجًا كَأَنَّمَا يَصَّعَّدُ فِي السَّمَاءِ كَذَلِكَ يَجْعَلُ اللَّهُ الرِّجْسَ عَلَى الَّذِينَ لَا يُؤْمِنُونَ ﴿۱۲۵﴾ وَهَذَا صِرَاطُ رَبِّكَ مُسْتَقِيمًا قَدْ فَصَّلْنَا الْآيَاتِ لِقَوْمٍ يَذَّكَّرُونَ ﴿۱۲۶﴾

﴾125﴿ Famai yuridil laahu ai yahdiyahoo yashrah sadrahoo lil islaami wa mai yurid ai yudillahoo yaj'al sadrahoo daiyiqan harajan ka annamaa yassa' 'adu fis samaaa'; kazaalika yaj'alul laahur rijsa 'alal lazeena laa yu'minoon
﴾126﴿ Wa haazaa siraatu Rabbika Mustaqeemaa; qad fassalnal Aayaati liqawminy yazzakkaroon

﴾125﴿ So whoever Allah wills to guide, He opens his heart to Islam. And whoever He wills to misguide, He makes his heart constricted and distressed, as if he were ascending to the sky. Thus does Allah place defilement upon those who do not believe.
﴾126﴿ And this (Qur’an) is the path of your Lord—straight. Indeed, We have detailed the verses for a people who take heed.

[125] This explains the benefit of true prophethood and highlights the contrast between two groups of elite individuals. Allah the Exalted, when He intends to guide someone, gives that person three signs—as mentioned in hadith:
1. Turning eagerly toward Paradise,
2. Renouncing the world,
3. Preparing for death before it arrives.
Such a person is then taught tawḥīd (monotheism) and the Sunnah, doubts are removed from his heart, and the duties of religion are made easy for him. These three qualities are what constitute sharḥ al-ṣadr (expansion of the chest).
But for someone who desires misguidance, just hearing about tawḥīd and the Sunnah causes his chest to tighten, his anger to flare up, and accepting the truth becomes extremely difficult for him—like someone forced to climb a steep hill or mountain. This is a simile showing that faith cannot enter such a heart.
(حَرَجًا) – With a fatḥah on the rā’ (حَرَج), it means “constriction”; with a kasrah (حِرَج), it means “extreme tightness.”
(كَأَنَّمَا يَصَّعَّدُ) – Ibn Jarīr said this is a metaphor: just as a person cannot ascend into the sky, similarly, faith cannot enter such a person’s heart.
(كَذَلِكَ يَجْعَلُ اللَّهُ الرِّجْسَ) – Just as Allah makes the person’s chest tight, He also casts rijs (defilement) upon them. According to Zajjāj, rijs means laʿnah (curse) in this world and punishment in the Hereafter.
[126] This verse is an encouragement toward the Qur'an, following the mention of the way of the misguided. Since earlier "يَشْرَحْ صَدْرَهُ" (He opens his chest) was mentioned, now the cause of that chest-opening is being explained.
The word (هَذَا) refers to the clarity and content of the Qur'an.
(الْآيَاتِ) – Refers to the Qur'anic verses, which are distinct and separate from each other—each addressing specific issues and themes. Every verse is independent in meaning and guidance, providing clarity on its respective topic.