Reading #1 Question

Throughout the essay, Benjamin is trying to describe how the introduction of film into the society of art has changed both the definition of art and the observance of the audience.  Why is it that the concept of reproduction of art in older times vs. modern times and the topic of architecture are elaborated in just as much, if not more, detail than his thesis?  Such as in the example of surgeon and magician, why does Benjamin wish to compare painting and film as if they were of equal standing and thus prove one "penetrates" the viewer more than the other?