The wizarding world intrudes on the Dursley’s comfortable emptiness with nothing-more-dangerous-looking than a letter in an envelope. The power of the written word is enough to drive the Dursleys onto a stormy island shack and Vernon to madness. The study in contrast between the wizarding world (the good part of it) and the Muggle world (the bad part of it) is painted in this chapter as the power of the written word (the letter) vs. the power of physical force (the knobbly stick).