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Surah 6. Al-An'am
Ayah 125 - 127
125فَمَن يُرِدِ ٱللَّهُ أَن يَهْدِيَهُۥ يَشْرَحْ صَدْرَهُۥ لِلْإِسْلَـٰمِ ۖ وَمَن يُرِدْ أَن يُضِلَّهُۥ يَجْعَلْ صَدْرَهُۥ ضَيِّقًا حَرَجًا كَأَنَّمَا يَصَّعَّدُ فِى ٱلسَّمَآءِ ۚ كَذَٰلِكَ يَجْعَلُ ٱللَّهُ ٱلرِّجْسَ عَلَى ٱلَّذِينَ لَا يُؤْمِنُونَ
126وَهَـٰذَا صِرَٰطُ رَبِّكَ مُسْتَقِيمًا ۗ قَدْ فَصَّلْنَا ٱلْـَٔايَـٰتِ لِقَوْمٍ يَذَّكَّرُونَ
127لَهُمْ دَارُ ٱلسَّلَـٰمِ عِندَ رَبِّهِمْ ۖ وَهُوَ وَلِيُّهُم بِمَا كَانُوا۟ يَعْمَلُونَ
[125-127] So (the fact is that) whomsoever Allah wills to guide aright, He makes his breast wide open to Islam,92 and whomsoever He wills to let go astray, He makes his breast narrow and squeezes it so tight that (at the very idea of Islam) he begins to feel as if his soul were climbing up towards the sky. Thus Allah sets the impurity (caused by their deviation from the Way of Islam) over those who do not believe, whereas this Way is the Straight Way of your Lord, and We have made its signs quite clear for those who are amenable to advice. There is an abode of peace93 for them with their Lord, and He is their Protector because of the good works they are doing.
92"He makes his breast wide open to Islam" means: "Allah makes him fully convinced of the truth of Islam by removing from his mind and heart every kind of doubt, suspicion, hesitation and indecision about Islam."
93"Abode of peace": Heaven, the place of perfect peace and happiness, where the dwellers will be immune from every kind of calamity and misery.