This is a famous Japanese novel and is highly recommended to read in Japanese literature. I watched and listened to a few book reviewers on Youtube and it did sound interesting. So I borrowed a copy from my local library. 
I read the book within a day. It is short and easy to read. I was hooked from the start. The writing and story is unique. As a reader, you get to understand and empathise with Keiko (protagonist).
My interpretation of the story is that Keiko's safe place is the Convenient store. The Convenient store for her is a controlled environment, it gives her purpose and routine. She becomes institutionalised, she becomes part of the store. She has been pressured to follow Japanese society ideals by getting married and having children. But it didn’t feel suitable for her. 

I recommend also watching the interview of Sayaka Murata on Japan Society channel on Youtube: https://youtu.be/5Eag3-URh2I