I find first pages of a book as the most instructive ones for many reasons. When I look into a good book which I've read many years ago, I still find those first pages more interesting and inspiring.
Recently, I started reading a new book: "A Book of Abstract Algebra". Similarly, I found a very interesting statement in the introductory chapter:
Algebra at the more advanced level is often described as modern or abstract algebra. In fact, both of these descriptions are partly misleading. [...] To what extent is it abstract? Well, abstraction is all relative; one person's abstraction is another person's bread and butter.
-- Charles C Pinter, A Book of Abstract Algebra: Second Edition, pp. 1-2.
It is, indeed. Obviously, there is a lot to think on the abstraction of abstraction.