Sometimes we think of the laws of Shabbat as dictated to us, either from the days of creation, or Sinai or even in the halls of the great seminaries in Babylon and Israel. Yet Shabbat 78 emphasizes that the laws are designed to respond to human needs and habits. And when and where those change, the laws change too.
Some halachot are set by the rabbis’ understanding human behavior. For example, when considering how much water may be carried into the public domain on Shabbat, the Gemara first asks whether the water is used for drinking or healing. If water is used for healing, a very small amount is necessary, and thus only a tiny amount of water would be permitted. (Of course if this were to save someone’s life it would be permitted on the grounds of pikuach nefesh.) If water is not used for healing, in general, then only a larger amount — the amount you need to take a gulp — would be prohibited. This turned out to be a regional difference:
Abaye says: We are talking about in the Galilee. In the happy Galilee people drank mostly wine, and water was used for healing. So in the Galilee, based on what people did, the prohibition of carrying water was very strict a very small amount would be prohibited on Shabbat. Elsewhere, where people perhaps did not live such a fun life as in the Galilee (or France?) since water was used mostly for quenching thirst, only a larger amount would be prohibited.
Eventually, Shmuel is quoted as saying that water is valued for healing eyes all over the world, and therefore the smaller amount — enough water to heal an eye — is prohibited everywhere.
The rabbis not only look at general human practices, which are sometimes universal and sometimes vary from region to region, they also ask whether what is carried from domain to domain has particular interest to the individual carrier. The Hebrew terminology signals when the interest has shifted to the individual. The term motzi (מוציא) – “one who carries out” – is used when looking at the general population: what is a significant, valuable amount of substance to most people? Based on that, you cannot carry that amount from a private domain to a public domain. However, the term matzni’a (מצניע) – “one who stores” – refers to the amount of substance that an individual values, which can be a much smaller amount, if it is important for some reason to that particular person. Then, for that person, even the tiniest amount of the valued substance should not be carried from domain to domain.
Shabbat, in the view of the rabbis, was not created for angels. It was a gift to human beings to help protect us from the work of the week. And we, as human beings, help determine how that protection is provided and implemented.