עד כל ימי הארץ זרע וקציר וקר וחם וקיץ וחרף ויום ולילה לא ישבתו ... (ח-כב)
In the aftermath of the מבול, Hashem promised that the seasons, night and day, will not cease to exist. Things will forever run in their “natural” fashion. The Gemara (Sanhedrin 58b) derives a halacha from this posuk: "ואר"ל עכו"ם ששבת חייב מיתה שנא' יום ולילה לא ישבתו ... אמר רבינא ואפי' שני בשבת" - Reish Lakish says that a goy who keeps Shabbos is חייב מיתה. Rashi explains that the posuk isn’t solely referring to the מזלות, sun and moon but to people as well. They mustn’t remain idle for a 24-hour period. Ravina says that this prohibition isn’t limited to our Shabbos, but even on a random Monday people may not abstain from work.
Why did Reish Lakish feel the need to also apply this to all to mankind; the posuk is referring to the world, not people. Also, why only after the מבול was this edict enforced? Lastly, according to Ravina that it’s applicable any day of the week, what is the meaning of this din? If it’s only applicable on our Shabbos we can understand it, because Shabbos is reserved specifically for us, Hashem’s children. But why should a random Tuesday pose a problem? (see Emes L’Yaakov)
Perhaps the idea is as follows. When Hashem created the world, everyone easily recognized His presence, His total command and control over its existence. After the deluge, Hashem altered the actual nature of the universe. Now the world would function על פי טבע, the sun would rise and set at predetermined times, after which the moon would appear. A gentile’s existence is also a natural one. Therefore, by him not working is the antithesis of his DNA. A Yid on the other hand lives his life שלא ע"פ דרך הטבע. Our entire existence is miraculous. Shabbos is our day with Hashem, where everything ceases to exist and is then created anew. It is in essence, a touch of "מעין עולם הבא". Thus, we strive to connect with that, while a goy cannot. Ravina came along and said that this idea that a person doesn’t work on any random day but relies on Hashem to provide him is also a chiddush that only us Yidden can live by, and therefore גוי ששבת חייב מיתה. "אין לנו על מי להשען אלא על אבינו שבשמים"