(And indeed it) means: the Qur'an, (is a cause of regret for the disbelievers) on the Day of Resurrection, for they did not believe in it during their worldly life.
﴿وَإنَّهُ﴾ يَعْنِي: الْقُرْآنَ ﴿لَحَسْرَةٌ عَلَى الْكَافِرِينَ﴾ يَوْمَ الْقِيَامَةِ، إِذْ لَمْ يُؤْمِنُوا بِهِ فِي الدُّنْيَا
