Many things in the "Law of Moses" had their origin long before Moses was even born. For example the animal sacrifices. They originated at the fall of man. Another example would be circumcision. Even though it was in the Law of Moses, it didn't originate with Moses, but with Abraham. In the Law of Moses there were also laws about marriage, but marriage originated before sin.
So the Sabbath of creation is the same as the Sabbath that is in the Law of Moses.
It says that God rested on the seventh day of the week. Does He need rest? Not according to Scripture:
Thus God doesn't get tired and doesn't have any need to rest. Why did He rest on the seventh day? There is an interesting verse in Ephesians:
The word "follower" there, in Greek, is μιμητής (G3402, mimētēs,
mim-ay-tace'), and it literally means
imitator, because it comes from G3401 which means "to imitate".
So what that passage is saying is this: "
imitate God as beloved children".
This is why God rested. According to Isaiah He doesn't need rest. So He rested to give us an example, to imitate Him.
It's easy to understand, really. The Sabbath was made before sin entered trough Adam. Before sin God also, besides the Sabbath, gave man the woman; thus He also created marriage. Do men still need women? Do we still need marriage? Of course. Do we still need the Sabbath? Obviously.
So the Sabbath of Genesis is the same as the Sabbath that is in the Law of Moses.