{So if they deny you, then say, 'Your Lord is possessor of vast mercy'} for whoever repents from his polytheism and accepts what Allah has revealed, {and His punishment cannot be repelled} meaning, His torment cannot be averted {from the criminal people}, the polytheists.
﴿فَإِنْ كَذَّبُوكَ فَقُلْ رَبُّكُمْ ذُو رَحْمَة وَاسِعَة﴾ لِمَنْ تَابَ مِنْ شِرْكِهِ، وَقَبِلَ مَا أَنْزَلَ اللَّهُ ﴿وَلا يُرَدُّ بأسه﴾ أَيْ: لَا يُصْرَفُ عَذَابُهُ ﴿عَنِ الْقَوْم الْمُجْرمين﴾ الْمُشْركين.