Family dynamics and community
In the most literal sense, this novel is just about family. The narrator turns out to be the young son of Christina, one of five sisters, a boy named Michael. There are men in the family as well, but they are rarely around. Michael's uncle Jack is a Ugandan missionary around whom there is some hint of scandal, and Michael's dad is a wayward man without a clear direction in life. For now he sells gramophones. Why is Michael telling us all of this? Because his identity is shaped by his family dynamic and community. This can also be seen as an allegory of family duty.
Expectations and duty
If the reader abstracts the plot of this novel to see what other kinds of meaning it might have, they will quickly see an unspoken expectation among the family members (especially the sisters) that everyone has a role in their family. This role is shaped around sacrifice: Kate's professional career is a sacrifice to her family, and her income supports the whole house, more or less. Agnes and Rose also sacrifice to help earn what little income they can, and the other two sisters take care of the housekeeping chores. Michael is left confused about his own relationship to family duty because all the men in his family seem to have abandoned their post.
Belief and religion
The thematic idea of sacrifice and identity is paralleled by a similar discussion of religious belief. This secondary theme underscores the ethical and moral nature of family duty, sometimes called filial piety. This other kind of piety is seen most clearly in Jack's story. Jack is a missionary in Uganda for decades, but now he has returned. Some people suggest that he fell out of the Irish Catholic faith of his childhood to prefer some sort of pagan mysticism. That shows a dynamic contrast in his religious belief; the more obedient he became to a group, the more individualized his identity became. That is a parallel to Michael's own adult feelings of detachment from family.
