That's not Biblical. Read Mark 2:27 “The Sabbath was made for man, and not man for the Sabbath”. It does not say the Sabbath was made for Jews but for mankind.
Ah, note I did not say Gentiles could not keep the Sabbath, nor that it wasn’t a good idea.
The OBLIGATION, however, to keeping the Sabbath only applies to the Jewish people.
The OBLIGATION (the mitzvah; command; contract term) first appears at Mt. Sinai, Exodus 31.13
“Speak thou also unto the children of Israel, saying: Verily ye shall keep My sabbaths, for it is a sign between Me and you throughout your generations, that ye may know that I am the LORD who sanctify you.”