It's a New Covenant vs. Old Covenant issue.
The seventh day is to be observed as the sabbath "throughout their generations, for a perpetual covenant".
Wherefore the children of Israel shall keep the sabbath, to observe the sabbath throughout their generations, for a perpetual covenant.
It is a sign between Me and the children of Israel for ever; for in six days the LORD made heaven and earth, and on the seventh day He ceased from work and rested. (Exodus 31:16-17)