Symbolism, Imagery, Allegory
When Joe and Peter are serving in Europe together during WWII, they come across a suitcase of gold dust and decide to transport it back to the States in order to grant themselves a windfall as they start their lives in America again. As Peter explains to Evie:
"And Joe knew about this suitcase full of gold. Gold dust. And what were we going to do, just let the army take it? By this time, you see, we were thinking about going home, and what we were going back to." (20.47)
The suitcase of money is supposed to represent a fresh start for Joe and Peter—happier days ahead, if you will—but it ends up weighing everyone down and causing plenty of problems. So the gold dust goes from representing hope and possibility, to signifying failed dreams, disappointment, and a major mess.
The money causes the rift between Joe and Peter, and it seems like it eventually leads to Peter's death (assuming it wasn't actually an accident). Evie realizes that even though Joe wants to use the money to buy them a new house once they get home, doing so will only destroy them. Because of this, she ends up giving the money to Mrs. Grayson in the end. It should go back to the people it was taken from—Jewish families—and used to help people from the Jewish community rebuild their lives after the war.
This decision on Evie's part to take the money and give it to Mrs. Grayson adds one more symbolic layer to this suitcase of gold. It is part of a shining moment for Evie in her personal evolution, and as such, not only also represents her breaking away from her parents to come into her own, but also when she does, she does so as a better person than the people who raised her.