Determining the author's purpose: What is the author trying to teach us?

Sooooooo...my little darlings are having a difficult time figuring out why the author wrote the book, and if he's trying to teach us a lesson.   Planning is rough when you only have twenty minute increments to teach such a difficult concept, and for these students, I really have to model and break down the thinking process.  So....here goes...gulp...

I first made an anchor chart with the direct teaching point that authors write for a reason: