Some of the major themes of Emma Donoghue's Room include the close bond between mother and child, the sacrifices mothers are willing to make for their children, survival and hope despite extreme circumstances, the difficulties involved in recovering from extreme trauma, and the journey from innocence to enlightenment.
I will begin with the last one I listed. Donoghue has young Jack narrate the novel. He is a child who has lived his entire life, unknowingly, in captivity with his mother, who was abducted years ago by the man who owns the house. Jack and Ma live in a shed behind the house, and the world he has grown up in, inside that small room, is all he knows. His narrative perspective is necessarily innocent and naive. He has no idea of the depravity of the outside world or that his father is the man who kidnapped and raped his mother. Gradually, the plot progresses so that Jack and his mom escape, and then he begins to learn more about the dangers of the world in which he lives, as he must now adjust to an entirely new reality.
The premise of the novel, as mentioned in the previous paragraph, gives way to some of the other themes I listed. Ma feels the need to protect Jack, so she invents a world for him that seems safe and harmless. She dotes on him and lives her life basically to keep him alive and out of harm's way. She sacrifices her own well-being in some ways by forcing herself to repeat the distorted truths that she feels she must teach her son. Once Ma and Jack escape, we see how much Ma struggles to readjust to life in the "real world" with her family. She is depressed and suicidal. It takes time and treatment for her to feel like herself again and after such an extreme lifestyle change. Throughout their time in the "room" and their time returning to the outside world, Ma and Jack fight and maintain hope as they try to survive. The novel is ultimately a testament to the human will to survive and the unbreakable bond between mother and child.