This is kind of an odd question, as I cannot really tell what its intentis. "Affect your understanding" is the phrase which is unclear. This question no doubt came from one of your professors, so it may not be particularly clear to you, either. It seems to me the question is asking how knowing about Holmes's murders impacts one's reading of the rest of the story. If so, there is really only one overarching idea--the darkest black makes the white seem even whiter. Here we have a consistent contrast between the very worst in human nature and the loftiest inventions and architectural wonders the human mind could create. The force of self-centered evil (Holmes) is the antithesis of Burnham's selfess achievement. Murder (taking a life) is even more horrible when we know that across town there is a magnificent celebration of life. What happens in the hidden rooms of a boarding house is even more sinister when contrasted with the grand Fair glistening in the open air for the entire world to see. These concurrent, parallel events serve to magnify and intensify each other. Perhaps this answers your question.