Underlining something in your book is the original “interactive” media. Think of it as a hyperlink that redirects to your own thoughts, and like a hyperlink, it can leave the rest of the story behind and open up a new window of ideas, insights, musings.
(Indeed, a point Mortimer Adler made in 1940.)
Evan Robertson takes snippets of text and ideas from some of his favorite authors and let the words be a springboard for an illustration. Brilliant.