For some reason ever since I read this quote it keeps coming back to me in that head-slapping "Of course!" sort of way. There's the obvious encouragement to show not tell in there, but it also seems like there's a bit more bundled up into that sentence.
I think one of the things that writers struggle against is the fact that it's all been said before. A thousand writers have described a thousand moons. We've described it--and many other things--so much that the descriptions have little meaning anymore. We skip over them thinking, "Right. Moon in the sky. Got it." It's like a word you repeat so many times that it loses it's meaning.
What's the purpose of description anyway? Certainly, description for description's sake is meaningless, isn't it? Who cares if there is or isn't a moon in the sky when a scene happens? The literal presence of the moon doesn't matter, what matters is how your description of the moon enhances a scene's mood or action, or metaphorical weight. So if the way we write about the moon causes readers to skip over it without considering it or feeling it, then the moon means nothing, its just there.
To get around that we need to surprise the reader. We need to make them see the moon in a different way, from a different angle, so that it will mean something to them again, so it won't just be background. In a way, we have to trick readers into really seeing the moon again.
This reminds me of a story I read not long ago (I'd cite it, if only I could remember who said it) about the usefulness of that strange lamppost the Pevensie children encounter sitting out in the middle of the woods in the Narnia books. This writer said that one of the functions of that lamppost was that the strangeness of its presence shocks us out of our familiarity with a forest scene and makes us see it fresh. Again, an unexpected detail, like the moon reflected in broken glass, can make us see familiar things like they're new again.
To dip into my theatre nerd background for a second, this is something like what playwright Bertolt Brecht called the "alienation effect" or the "defamiliarization effect." Brecht wrote that this involved "stripping an event of its self-evident, familiar, obvious quality and creating a sense of astonishment and curiosity about it".
Isn't that what we all want to do? Create "a sense of astonishment and curiosity" that will shake people out of their routine and make them see and consider familiar things in new ways?