Or HaChaim on Exodus 20:9/אור החיים על שמות כ׳:ט׳

1 ששת ימים תעבוד, "During six days you shall labour, etc." Seeing that the Torah also speaks about "and you shall do all your work," what exactly did G'd mean when He said: "you shall labour during six days?" We may have to understand this in terms of Leviticus 25,20-21. The Torah quotes the Jewish farmer who has been asked to observe the Shmittah year as asking in the seventh year: "what shall we eat?" The Torah there answers that G'd will command the earth to supply sufficient harvests during the sixth year to last for three years. This is exactly what G'd alludes to here. When the Torah commanded us to keep the Sabbath holy this means that no profane matters are to be performed on the Sabbath. If so, seeing that most people perform enough work on one day to feed themselves on that day, what are they to eat on the Sabbath? G'd answers: "you shall labour for six days and do all your work." The clear implication is that the amount of work you perform on the six days will produce your needs also for the Sabbath. G'd assures those who keep His commandments that they will not suffer any hardship as a result.

2Another aspect of the phrase ששת ימים is that once the Sabbath arrives you are to feel that the work week is over; you are not to think about work you have not been able to complete last week and have to continue next week, etc. The domain called ששת ימים and the domain called שבת are mutually exclusive. The author refers the reader to a story related in Shabbat 150 of someone who imposed a penalty on himself for having contemplated repairing a fence which had collapsed on the Sabbath. As a result of his decision not to repair the fence and thereby to expose himself to serious financial loss, a miracle happened and in the place where the break had occurred a caper bush grew which provided him and his family with an adequate income forthwith so that he did not need to restore the breach in the fence.