You really, really didn't understand Galatians. Very little in the Bible even singles out the Ten Commandments as "special", much less "applicable to all Christians".
Their applicability to all Christians was established by the Church as a teaching point because they codify natural (moral) law, which is applicable to all human beings, and was applicable even before the Ten Commandments were given to Moses.
However, you can't get a Saturday Sabbath from natural law -- you need revelation for that -- so it is not part of the moral law, but part of the ceremonial law. Even the rabbis agree that keeping Shabbat is not required of or even permitted to Gentiles.
You mean like God coming down and writing it with His finger in stone? That kind of revelation?