Word by Word Analysis

وَمَن كَفَرَ فَلَا يَحْزُنكَ كُفْرُهُۥٓ ۚ إِلَيْنَا مَرْجِعُهُمْ فَنُنَبِّئُهُم بِمَا عَمِلُوٓا۟ ۚ إِنَّ ٱللَّهَ عَلِيمٌۢ بِذَاتِ ٱلصُّدُورِ 23

And whoever has disbelieved - let not his disbelief grieve you. To Us is their return, and We will inform them of what they did. Indeed, Allāh is Knowing of that within the breasts.