What is the theme in Please Look After Mom by Kyung-Sook Shin?

On a fundamental level, the novel's primary thematic focus is on the question of what it means to be a mother. Even though most of the central characters (and three of the narrators) are not themselves mothers, their experiences, and their reflections on those experiences, are for the most part defined by what they believe a mother's responsibility is. Those beliefs are, in turn, defined by the attitudes and beliefs of the mother figure in their lives, HER beliefs in turn defined by the beliefs of her mother.