{A Book revealed unto you}, meaning: the Quran.
{So let there be no constriction in your chest because of it}, meaning: doubt that it is from Allah.
Muhammad said: The root of al-haraj is constriction, and one who doubts a matter feels his chest constricted by it; therefore, doubt was termed haraj. {That you may warn thereby} against the Fire, {and as a reminder to the believers}, they are reminded of the Hereafter by it.
﴿كتاب أنزل إِلَيْك﴾ يَعْنِي: الْقُرْآنَ.
﴿فَلا يَكُنْ فِي صدرك حرج مِنْهُ﴾ أَيْ: شَكٌّ بِأَنَّهُ مِنْ عِنْدِ اللَّهِ.
قَالَ محمدٌ: أَصْلُ الْحَرَجِ: الضِّيقُ، وَالشَّاكُّ فِي الْأَمْرِ يَضِيقُ بِهِ صَدْرًا؛ فَسُمِّيَ الشَّكُّ حَرَجًا ﴿لتنذر بِهِ﴾ من النَّار ﴿وذكرى للْمُؤْمِنين﴾ يذكرُونَ بِهِ الْآخِرَة.
