I don't really know what the question was, but if you are looking for the definition of the "author's purpose", then here it is.
Depending on the purpose, authors may choose all different sorts of writing formats, genres and vernacular. A simple trick to summarize the three main categories of author's purpose is to use the acronym PIE, which stands for persuade, inform and entertain.
I don't know if this answered your question, but I hoped this helped. c;