Looking for something else in Pinchas Peli's Shabbat Shalom, I stumbled across a teaching I had marked long ago and forgotten about. Even though we're past the week of Parashat Bereishit, a little teaching about the story of Creation is never a bad thing, so...
When God creates the world, we keep reading that "God saw that it was good." But, when God creates Shabbat, we are told that "God made Shabbat holy."
Peli teaches that this distinction is deliberate. The world, as it is, is good. Once it's created, it's good. We can appreciate it, or not, but it will always be good.
But, holy? Holy is different. Holy is something which has to be created. And, not just once, by God, but over and over again, by us, in partnership with God.