Andrew's study is a site of some major transformations throughout the novel. Andrew has being doing research on asylum seekers and immigration detention centers since he met Little Bee in Nigeria. After his death, when Sarah finds his research in the study, she believes he was trying to write a book (somehow never told his wife about this, but whatever). This knowledge certainly transforms Sarah's feelings (and maybe the readers') toward Andrew. It also changes her life as she tries to pick up this incredible book project where he left off.
Andrew really tries to transform his study into a vehicle for helping people like Little Bee, whom he believes is dead, and whose death he thinks he's responsible for. Hanging himself in his study could be seen as a symbol of his loss of faith in books, in the written word, to make a positive, real difference in the world. Sarah's decision to continue Andrew's work could represent a renewed faith in all this writing business – research, storytelling, and words in general – as ways to help others.