Since the Bible says that it was at Mt. Sinai (more than 2,500 years after the six days of Creation) that God “made known” His “holy Sabbath” (Neh. 9:13-14), then the observance of the Sabbath as a “holy day” was/is not an eternal, perpetual law going all the way back to Creation.
Since the command to “Observe the Sabbath day, to keep it holy” (Deut. 5:12) was given to Israel, when “God made a covenant with [them] in Horeb (i.e., Sinai)” (Deut. 5:1-2), then it (along with the rest of the old covenant) was not a universal law given to all man for all time.
Since the Ten Commandments were, in all respects, part of the old covenant (1 Kgs. 8:9, 21), and since we are dead to that law (clearly taught in Romans 7:1-7), then Christians today are not bound by a law that was made only with Jews more than two millennia ago.
Since Jesus took “away the first [covenant] that He may establish the second [covenant]” (Heb. 10:9), and since His New Testament does not authorize Sabbath keeping but does authorize the first day of the week, then we must obey that for which we have authority (Col. 3:17).