| Quote #1
The delivery boy was sixty-two years old, and there was no such person as Barney Northrup. (1.4)
It's pretty unusual to find out that a character doesn't really exist, right after we've met him or her. The fact that Raskin gives this idea up so early in the text suggests that there are far greater mysteries at work. While usually the fact that someone's totally constructed an imaginary identity could be a huge reveal at the end of a text, here it merely sets the tone for the many identity-related surprises to come.
| Quote #2
Who were these people, these specially selected tenants? They were mothers and fathers and children. A dressmaker, a secretary, an inventor, a doctor, a judge. And, oh yes, one was a bookie, one was a burglar, one was a bomber, and one was a mistake. (1.32)
It's neat to think about how we can have more than one identity at a time. You can be a father, a bookie, and a doctor, for example, but while you may flaunt some aspects, you might wish to keep others secret. That's part of what makes this mystery so interesting, and complicates the usual mystery's idea of the whodunit. In this case, we don't know who any of these people are.
| Quote #3
Grace Windsor Wexler wrote housewife, crossed it out, wrote decorator, crossed it out, and wrote heiress. (4.38)
While some of the other heirs agonize over what to write, and some don't even hesitate, Grace is the only one to re-write it on the form. As Grace fluctuates between these three positions, we see her go from what she actually is (a "housewife") to what she's currently pretending to be (a "decorator") to what she thinks she deserves to be (an "heiress").