Shabbat is defined by what stops, and the stopping is technically specified: the thirty-nine categories of creative work derived from the labors used to build the Tabernacle — sowing, writing, kindling, carrying, and so on. That derivation explains why the modern applications look strange from outside (electricity, elevators, phones) and coherent from inside: the question is never "is this effortful?" but "is this a species of creative work?" The theological frame is that a person spends six days shaping the world and one day declining to, as a weekly refusal to be defined by production.