It's a really good depiction of what it's like to lose someone. There's nothing religious to it, nothing existential, just a very relatable depiction of the pain you feel when someone dies.
Message
You don't have to forget those who died in order to live your life. You can keep the memory of them alive.
There's not a lot to it, but it doesn't seem like it's trying to be more than it is. It kind of has a dreamlike quality to it, as the words swirl around the pages, and the images are almost like sketches rather than full-on realism.
It's kind of unusual, with pages that fold out in different directions. The artwork is very charming. There's not a lot to it, but it's the kind of repetitive that is endearing rather than mind-numbing.
It's just fun. There's nothing really to it, and no real point. But it captures the feel, at least as far as an outsider can, of the mind of a young child who is walking but not yet speaking in complete sentences.
The kid being obsessed with something like that is very realistic, especially nighttime rituals, but the girl is demanding something that doesn't exist.
It's a recognition of the important role that pets play in people's lives, understanding that just as it's difficult for children to accept new siblings, it's also difficult for the pets to accept it.