My son just sent me this list of quotes from Time Enough For Love, my favorite Heinlein book, which was first published in 1973. What's striking about them, looking at them now, is how timeless many of his observations about human nature are.
The title of the book refers to the lifespan of Lazarus Long, who was born in early twentieth century America -- like Heinlein -- but who lives for two thousand years, after which he no longer has any desire to live. The book is always listed under the category of sci-fi. But it has all the ingredients of any great book: it's romantic, adventurous, sentimental, and practical, all at the same time.
It certainly moved me when I read it in 1974.
(In fact, I may have just talked myself into re-reading it.)