This question refers to the book Eiger Dreams, written by Jon Krakauer and published in 1990.
The correct answer is these chapters increase his credibility for writing his book.
The mentioned chapters increases his credibility once they make clear the author's concern for his readers by showing details from his adventures and exposing his passions and opinions about a topic in which he is passionate about. This shows how open to criticism and responsible Krakauer is on his book.