Sforno on Exodus
ושמרו במי ישראל את השבת, in this life, לעשות את השבת, on a day that is totally Shabbat. [the afterlife. Ed]
Or HaChaim on Exodus
ושמרו בני ישראל את השבת, "The children of Israel shall observe the Sabbath, etc." Why did the Torah add another "observance?" Besides, why does the Torah use the verb לעשות, "to do," which expresses an activity when the meaning seems to be that the children of Israel are to observe the Sabbath by "abstaining" from a number of activities? Our sages have pursued their own path in explaining this wording.