Symbolism, Imagery, Allegory
At first, the shelving Renfrew puts up for Marjorie to store preserves on seems like a throwaway image, just some action to get Chapter 10 started. But then the imagery comes up again and again… and again. And that, dear Shmoopers, is one way to know you've got yourself a symbol on your hands.
The shelving represents the merging of the mathematical precision of science, our much messier everyday reality, and human perception of the truth when faced with both. Consider this moment when Renfrew first completes the shelves and admires his work:
He stepped back from the tilting walls, squinted, and saw that the lines of his home were askew. You put down the money on a place, he reflected, and you get a maze of jambs and beams and cornices, all pushed slightly out of true by history. (10.2)
Marjorie argues that the shelves are crooked, but Renfrew says no—he built them "on a precise radial line extending dead to the center of the planet, geometrically impeccable and absolutely rational" (11.81). The shelves are mathematically accurate, but the world in which the shelves occupy—here represented by the house—is not. Time, weather, and people have slowly bent and twisted the house ever so slightly.
So which one is truly out of whack? That depends on how you look at it. When Renfrew first puts up the shelves, he feels the house is crooked and the shelves are accurate. But when he comes back to look at the shelves later, he realizes, "it was the shelves which stood aslant now; the walls were right" (10.81). So while the shelves may be technically correct, what we see here is the role perception plays in human understanding of things.
We see this same shift play out with Marjorie. When she first sees the shelves, she dismisses them as off kilter. But later, when she is drunk and being seduced by Peterson, Marjorie is in a heady place. The "room wave[s] and ripple[s], except for the straight shelves" (37.65) which "seemed more substantial now than the walls" (37.70). Even when dismissing the rest of the world as wobbly and inconsequential, the shelves remain true for Marjorie—which, of course, they are.
Just like Marjorie's perception of the shelves, human perception can change from time to time and feels relative. However, like the shelves, the truth always remains the truth, even if we can't see it at the time.