Symbolism, Imagery, Allegory
Ever come across an important heirloom or souvenir from a friend or family member? You probably felt a lot of emotions looking at it, from nostalgia to happiness to maybe a little bit of melancholy. Or maybe you felt what Stan feels when he discovers his mother's wedding dress in a trunk in his shed: regret. When he finds the dress, he flashes back to seeing it as a child and laughing at it along with his sister, saying it looked like "a nightie" (5.11). It's only now, as an old man, that he thinks of just how much the remark hurt must have hurt his mom.
Right off the bat, then, the wedding dress represents perspective. Stan sees both it and his behavior as a kid quite differently now than he did way back when, which reminds us as readers that thoughts, feelings, and opinions can all change. And Stan, of course, may be the character who shifts the most in this regard. So finding the dress sort of foreshadows some of the changes yet to come for Stan.
There's more to this garment, though. Like a strong family, the wedding dress is intricately and tightly woven. Stan observes this looking at the dress for the first time in years, "half expecting the beads to fall at his touch and scatter […] but they held fast, and he thought how things were made properly in those days, made to last" (5.15). Instead of feeling good when he finds the dress, though, Stan feels badly.
The discomfort he feels at finding the dress reflects his growing realization of his own family's troubles. His daughter is divorced, he and Lonnie aren't speaking, and his own mother and sister are both gone. "He wished he'd never found that wedding dress," he reflects later in the story. "Like a meal of bad oysters, it seemed to have unsettled him" (20.13). But while the dress is initially the cause of a mistake Stan wishes he could take back, it's ultimately what makes the family right again.
When May shows Lonnie the dress, he's struck by how it seems to be "made for" Clara—"except it belonged to Pop, and if Pop was a racist, as Lily said, then Clara would never get to wear it" (30.47). The awesome part, though, is that in spite of this, she does get to wear it. When the family reunites at Nan and Pop's at the end of the book, Clara tries on the dress, and it fits perfectly. So while the Samsons have gone through a lot of hard stuff, in the end we see that they, like the dress, are "made to last." Onward, Samsons.