Why SICP?

What's so good about SICP? Isn't LISP completely useless?

SICP is good because it teaches the essence of programming, rather than teaching you how to use a particular language.

Lambda calculus is essentially the mathematical soul of computing, and Lisp, at first, was basically just an executable version of that.  It grew larger over time and supported meta programming, so it could adapt to any new ideas that came along.

As has been mentioned, the variant of Lisp used in the SICP course is a pure subset called Scheme, which cleaves more exactly to the Lambda calculus, and has been deliberately kept small (scheme can be defined completely in 30 pages), so that their book, and the course they taught could focus more on teaching the essence of programming, not merely a programming language.