Thesis on Philosophy of History

I'd really like to focus on Benjamin's imagery of the Angel of History whose back is turned to the future and who faces history as he watches it pile up (This is what he calls progress). I wonder why he describes history as a pile of destruction but a destruction that is beneficial for our knowledge. He also talks about the angel being blown back not being able to return to history, I guess it is kind of like everything is forced to the future and can never really return in time.