story of the door

I want to spend this time talking about the story of the door and how it is significant. The story of the door is the opening story and the main thing that drew me into this strange plot was when a casual silent walk between Ulterson and Enfield turn into this crazy chase between a girl and a man. I am not going to lie when I began reading this story I was instantly bored with the plot but when a casual afternoon walk turned into what I first began to think was a crime scene I instantly changed my mind. It took me a minute to realize this story between a girl and a man was a flashback memory of Enfield. Once I realized this I was forced to ask myself why the door was so significant aside from the fact it brought back an intense memory of something that happened to a girl. Enfield states, "I was coming home from the end of the world" (Pg 834) that makes me think the door is a transeiting moment to where the plot changes from current day to a flashback. Overall I feel the significance of the door story is to bring about Ernfield as a main character as well as shed light on the type of society they live in where a man is instantly hated for his outside appearance. My main question is what else could the door represent and why did the author choose a door rather than a building.