It says, "Flee bachelors flee. If you would single stay. Tis Halloween eve, The witches wedding day!"
According to folklore, the angle of the window is supposed to prevent witches from entering the house (of course that begs the question about the other windows). Someone on one of my DIY shows suggested it was for getting a coffin out of the upstairs easier...but then why not just carry the body downstairs and put it in the coffin on the first floor? Anyway, the most likely reason I've seen is that Yankee ingenuity and frugality was the main reason for this cockeyed placement. This way a special sized window wouldn't have to be ordered (more expensive).