When this was first written, it was a matter of baking a loaf of bread and roasting a leg of lamb on the evening before and leaving the sheep in the pasture to take care of themselves. There was no such thing as basketball tournaments and organizational meetings and work deadlines.
Or perhaps, when it was first written, the author knew of the busy-ness that was coming. Of the competition that would occur each sabbath between taking time to rest and worship and shuffling to a sporting event or working on a project that was assigned weeks ago but is due tomorrow. Perhaps the author knew that we would need a divine excuse to say "no, I'm not available on Sunday" to the many committee meetings and birthday parties. Perhaps he knew that we would want a guilt-free way to step over the piles of laundry and leave them for tomorrow. He knew that after working and running all week long, we would be ready for a day to do nothing but reflect on the week we've made it through and mentally prepare for the week about to come. After having lived to see another sabbath, perhaps he thought we'd like pause and say "thanks".
The author gave us those options. Now it's up to us what we do with our day.