Shabbat 70 - Shabbat in a desert
If one was walking all alone in a desert, and one day he realized that he forgot which day is Shabbat, how is he to behave? - He must count six days, including the day on which he realizes his predicament, and then observe the seventh day as Shabbat.
Rava added that on every day he can only do as much labor as is needed to stay alive, because this might actually be Shabbat, and he can't desecreate it, even out of doubt. On the seventh day he does no labor. The Talmud asks, and on the seventh day he should die? - He should work twice as much on the day before! - But maybe the day before is Shabbat? Rather, he should work the same amount on every day. But then, how is Shabbat different? - Because he says the kiddush - prayer welcoming Shabbat - at the beginning of it, and the Havdallah - prayer welcoming weekdays - at the end.
Earlier we learned that if one knows that it is Shabbat and does multiple acts of prohibited work by mistake, he is liable for a sacrifice for each violation. Why should this be the case? - Because he brings a sacrifice for each mistake. - Still, why not say that this is all one mistake? - Because the Torah said, " One who violates Shabbat will die, he will die " - we see multiple punishments for multiple mistakes. But that is talking about one who violates Shabbat knowingly!? - That we already know from another verse , and therefore, since the new law is not needed for its own sake, let's apply it to another context, where he violates Shabbat by mistake. This proves it.
Art: Carl Haag - In the Desert