What was Lincoln missing from his drawer in the island?

In the context of the novel "Lincoln in the Bardo" by George Saunders, Lincoln is missing a sense of closure and understanding regarding his son, Willie, who has passed away. The drawer symbolizes the emotional and spiritual void left by his son's death, highlighting Lincoln's deep grief and the complexities of loss. This absence reflects the broader themes of mourning and the struggle to connect with loved ones who have departed.