Queen of the Castle has a brief summary up, if you haven't read this and want to know what the heck I'm talking about. :)
This is probably one of the first books I read that I counted as a "If the house was burning down, I would save this book." I first read it when I was 12, after having ordered it from our 7th grade book order. It's a thin, little green novella, with the title in raised gold print and a tiny white snowflake underneath. It is also looking a bit dog-eared by now.
Since the book is very short (under 70 pages), I tore through it on the bus ride home. And then I read it again. And again. And then one more time. And then I discovered he'd written more books. So since then, I have read them all: The Timepiece, The Letter, The Locket, the Looking Glass, the Carousel, The Last Promise, The Sunflower, Finding Noel and The Gift.
In short, I'm addicted to this author.
As both Nutmeg and Queen of the Castle say, if you are a parent, this book has a message for you--to cherish your children's childhood. To, as Richard says in one of his books, "wake up one morning and know that [they'll] be gone." But even if you don't have children, this applies to everyone--to stop and savor each moment, because you're not going to get it again. Every minute is so unique and precious and we need to realize that, instead of constantly thinking "oh when will this be over?" or "I can't wait until I'm________" (fill in with whatever you're waiting for).
I read this book every year at Christmas, and his other books all year round. It's simple message is inspiring.
For more on how R. P. Evans wrote the book, I recommend his autobiographical work, The Christmas Box Miracle.