(وَلَوْ تَرَىٰ) (And if you could see): Allah (swt) addresses His noble prophet (saws).
(إِذْ يَتَوَفَّى الَّذِينَ كَفَرُوا ۙ الْمَلَائِكَةُ) (When the angels take the souls of those who disbelieved.): Note that Allah (swt) does not state the apodosis of this conditional clause. It is omitted, thus left to the Prophet (saws) and other people to imagine the painful punishment that could happen, the last moment of extraction of the soul and what the angels of death do when taking out the soul of the disbeliever.
(يَضْرِبُونَ وُجُوهَهُمْ وَأَدْبَارَهُمْ) (They are striking their faces and their backs,): Here, a person’s imagination can’t grasp any scenario because it’s challenging to envision this situation and how the angels of death will strike the faces and backs of these disbelievers.
(وَذُوقُوا عَذَابَ الْحَرِيقِ) (Taste the punishment of the Burning Fire.): After this torment, the punishment of the fire will follow, and what a terrible fate it is.