I didn't read through the entirety of SICP, but I read through the first ~3 chapters, and it helped me to understand the way that functions are associated with

I didn't read through the entirety of SICP, but I read through the first ~3 chapters, and it helped me to understand the way that functions are associated with the environment that they are defined in and how this fact can be used to construct closures. I haven't seen as good of a description of this up until that point.