For all we know, God could have required the left cheek instead of the right earlobe. He could have required 10 percent less bread than he did. Since we do not know the divine significance of such details, they had to be given by special revelation. Even without God's special revelation to them, they might have had a concept of religious impurity, and from that developed a religious cleansing ritual, but they probably wouldn't have come up with the exact formula God gave them. Although the ceremonial laws portray concepts like sacrifice and cleansing that are found in many cultures, the details of God's ceremonial laws are given by special revelation, not by ideas that people could figure out for themselves.
Some people claim that the weekly Sabbath is a moral law, and therefore required today.
They often claim this simply because they assume that the Ten Commandments are all moral laws. He did not before creation, and he does not now. Angels do not keep the weekly Sabbath, either. In the new heavens and the new earth, when there is no nighttime, no one will have to change their behavior according to days of the week. Everyone will be in God's eternal rest all the time.