Sforno on Exodus 20:8/ספורנו על שמות כ׳:ח׳

1זכור את יום השבת, the infinitive mode tells us that we are to be aware of the Sabbath every day of the week, even while involved in our daily routines. This is also the same mode chosen by the Torah for demanding that we be forever mindful of what Amalek our arch enemy did to our forefathers after they had crossed the Sea on dry land. (Deuteronomy 25,17) The same is true of the infinitive mode chosen by the Torah when urging us to remember the legislation pertaining to the “month of spring,” i.e. the month of the redemption from Egypt. Compare Deuteronomy 16,1 שמור את חודש האביב ועשית פסח.

2לקדשו, the reminder to remember the Sabbath constantly was intended to ensure that you observe all the commandments associated with the day. Even the order to work six days is intended to ensure that by concentrating on the need to make a living during those days, this will enable such people to take their minds off such mundane matters on the Sabbath.