Divrei Torah on the weekly portions
"Remember the Shabbat day to keep it holy. For six days you should work and do ALL your Melachah*. But the seventh day is Shabbat to the Lord your God. Do not do ANY Melachah …" (Shemot 20:8-10).
The Vilna Gaon asks why the Torah includes the phrase "For six days you should work and do all your Melachah" when we could have easily deduced this ourselves from the next sentence which teaches that we may not do any Melachah on the seventh day? Additionally, since we know the Torah never wastes words, why mention the words "ALL" and "ANY" which appear to be superfluous?
There is a fascinating Gemara (Shabbat 69b) which discusses what to do if one is wandering in a desert and does not know what day it is! When should one observe Shabbat? The Gemara concludes that such a person should count six days and observe the seventh as Shabbat. During the six interim days (as well as the seventh), because of the doubt that one of them might be Shabbat, he is permitted to perform only enough Melachah to keep himself alive, but no more.#
The Vilna Gaon finds a hint to this law in the above verses of the commandment of observing Shabbat in the Ten Commandments. When the verse begins: "Remember the Shabbat day to keep it holy", the Torah is teaching that we must ensure we always remember which day is Shabbat, so that we will be able to do ALL our Melachah on the six weekdays. However, if we would forget which day is Shabbat then we would not be able to do ALL our Melachah on the other six days - we would only be allowed to perform enough Melachah to keep alive, but no more. This would not be ideal, physically.
The statement: "But the seventh day is Shabbat to the Lord your God. Do not do ANY Melachah" hints that if we ensure we always remember which day is Shabbat, then when Shabbat comes we will be able to rest from all forms of Melachah and not have to do "ANY" Melachah, not even Melachah necessary for keeping alive. However, if we would forget which day is Shabbat then we would not be able to rest from all forms of Melachah because we would need to do some Melachah to keep alive. This would not be ideal, spiritually.
* Melachah refers to 39 categories (Gemara Shabbat 73a) of creative or destructive work, which demonstrate man's mastery over nature.
# In practise, therefore, the only difference between the 7th day which we'd be considering to be Shabbat and the other 6 days which we consider to be weekdays is that on the 7th day we'd make Kiddush at the start and Havdallah at the end. Obviously, this Havdallah would not include lighting a flame, because maybe the 8th day (i.e. and also the 1st) was really the true Shabbat.