A reread can reveal how much of the first reading came from your circumstances.

Books do not change and readers do. Coming back to something after years, you find a passage you have no memory of and lose one you had underlined twice, which says more about the two versions of you than about the pages. The first reading was a collaboration between the book and whatever you were living through.

Reread something that mattered a decade ago and notice where the emphasis has moved. Ask what you needed then that you do not need now. It is one of the cheaper ways of measuring how far you have travelled.