What might be “holy” about resting (Gen 2:3)?

Perhaps nothing in itself. Certainly not every time a man rests is it a holy rest. But this demonstrated instance of resting was a holy example to man, who even before the Fall, here, is said to need one day in seven to rest. Insofar the day is set apart (the word for “holy,” קָדַשׁ or qadash, means something like “set apart”) from the other six unto God, and insofar as holy God himself “rested,” it makes sense that the Mosaic code, in the Ten Commandments itself, sets the sabbath as a holy requirement (Ex 20:8-11). Indeed, in the Decalogue, the text points back to God’s rest: “For in six days the Lord made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the Lord blessed the sabbath day, and hallowed it.”