If the Sabbath day is not binding on Christians why are we warned not to disobey in Hebrews 4?

Hebrews 4:9-11 ESV So then, there remains a Sabbath rest for the people of God, (10) for whoever has entered God's rest has also rested from his works as God did from his. (11) Let us therefore strive to enter that rest, so that no one may fall by the same sort of disobedience.