What is the correct interpretation of the Almighty's saying: (Some faces on that day shall be radiant, looking at their Lord; and other faces on that day shall be gloomy, thinking that some crushing calamity is about to be inflicted on them)?

The verse "Some faces that Day will be radiant, looking at their Lord" is interpreted to mean that the faces of thevers will be beautiful, bright, and joyful, and they will see their Lord with their own eyes, as indicated by the authentic and continuously narrated (mutawatir) hadiths. As for "And [other] faces, that Day, will be contorted, expecting that there will be done to them a backbreaking calamity," it refers to the faces of the disbelievers, which on the Day of Resurrection will be grim, their colors changed, and they will be certain that they are doomed and will enter the Fire.