Chris forgot a lot of life. That's the important detail of the plot, and it bears symbolic weight. It returns his opinions to a framework of genuine naïvete. He doesn't remember moving on from Margaret, being with Kitty, losing their son—none of that. This positions him in a strange point of view: He reassesses his own life without reference to memory. This serves as a symbolic portrait for what PTSD does to Chris.
The reason memory and trauma are connected is typically because trauma makes memories very chronically harmful (especially memories of war), but by happenstance, this novel is predicated on the opposite. Trauma erases fifteen years of Chris's personality. The trauma of his life literally makes him unable to relate to life the way he used to. He is changed by the trauma, and the detail of memory loss can be seen through that lens, as the symbol referring to those changes.
The women in Chris's community knew him both before and after. In some ways, Chris only knows himself before memory loss (which poses some unique romantic challenges for Margaret, to say the very least), and the reader only knows Chris post-war. The character is broken apart, and it's hard to know when the reader is getting a full picture of Chris. This symbolizes the difficulty of accepting him back into the fold of his own community, with his new damages and limitations.
