"Why are you reading that again?" My husband thinks it's crazy to re-read something when there are so many unread books sitting around the house. But some books are fun to revisit, like Gone with the Wind, required reading for girls growing up in Virginia. It's got war and sex and Scarlett O'Hara kicks butt (in her selfish, fiddle-dee-dee way). Sure, you know exactly what's going to happen, but that's the cool part - you're excited about what's coming next.
A few years ago we watched Tinker Tailor Soldier Spy with Gary Oldman and liked it very much. I'd read the book when I was younger and thought it was... well, dull. Back then I was into spy books with car chases and gun battles. And George Smiley - meh. But after seeing the movie, I read the book again and to my surprise, thought it was great. Middle-aged me fell in love with middle-aged, un-glamorous, brilliant, yet plodding George Smiley. He wasn't so dull after all.
To Kill a Mockingbird is another example. Most of us read that when we were young and identified with either Scout or Jem. (I was totally Scout - growing up in a small southern town, idolizing my father. I even had bangs.) Reading it when I was older and married with children, made me relate more to Atticus. I wondered how Atticus felt about the loss of his wife, about raising two children on his own. How hard was it for him to take the Tom Robinson case when he knew it would impact his children? Things I never considered when I read the book the first time.
The books stay the same, but we change. We can re-read to enjoy something familiar, something that's given us pleasure before. And we can discover new layers, new details we missed the first time around.