The author's choice of language sets the mood and tone of the work, and it shows the level of proficiency or experience the writer has. For example, if an author uses complex, dark language to portray the point of view of a small child, that wouldn't be a wise decision in most cases. Instead, they would use simple, positive language to portray the mind of the child more correctly. The author's choice of words, grammar and complexity, also shows how talented (or not talented) they are at writing. For example, if a writer tried to describe a haunting, cold, stormy scene using words such as "rain", "dark", and "cold", simple, non-descriptive word, it is most likely the case that they haven't had a lot of practice. If they used words like "deeply chilling", "frigid", "the wind howling through the trees", "gave him/her/them gooseflesh", etc., it i likely they are a more talented writer.
I hope that helped!
