For which purpose the author used the 1st person narrative?

It's an open secret that  from the point of view of presentation the text is the 1st person narrative. The author is the main character of the story. Charlotte Parkins used such kind of presentation to make the story more subjective and true-to life. When you read the book you feel, as you read the woman's thought, you are afraid ,you are laugh, you doing everything what the main character does.