Like author, like book.

The proverb suggests that a writer’s qualities may show through in their work. It treats the book as a reflection of the person responsible for it.

It can express recognition when a book seems consistent with what someone knows of its author. Depending on the judgment being made, that resemblance may be praise or criticism.

Use it to comment on a perceived resemblance between a writer and a book they have written. It works best when the speaker can point to a quality of the book that they also associate with the writer, rather than assuming that every feature of a book reveals its author.