Been a while since I read it but lets try and tl;dr it. Draco and his buddies stole the puzzle-box and opened it in a grand ceremony with all their purist buddies and got slaughtered like cattle, Draco got a special treat by eternally reliving a nightmare where he's blamed for all their deaths only to be woken up at the end just long enough for Pinhead to explain nothing of it was real and that he's really in Hell. And then they do it all over again, forever.

 

And Harry left the puzzle-box easy to steal and left clues that it is extremely important for him. So his enemies will steal it, open and end slaughtered by Pinhead and others. Later repeat entire thing.

 

I think I understand what you mean, did you read EBTMG? Everything that's happening makes more sense if you have the background that one provides.

 

For me it was perfectly clear even without EBTMG.