Rav Yakov (Bereishis 08:22) and day and night shall not cease.Sanhedrin (58b) An idolator who keeps Shabbos is liable to the death penalty because the Torah said “And day and night shall not cease.” Rashi explains that means they must continue working on Shabbos. Apparently, this interpretation is not according to the Bible's simple meaning (pshat) because the simple meaning is that G-d promises that the times and the seasons will not change so how is this connected to saying that an idolator who keeps Shabbos is liable to the death penalty? But it seems that the Gemara's intent is the depth of simple meaning of the verse. Here G-d revealed to us that the conduct of the world will be in a different way after the flood than it was before the flood. Before the flood G-d behaved with His world in such a way that it could be clearly understood that the world is new and is renewed in other words nature wasn’t fixed so it couldn’t be changed and thus it was clearly apparent that G-d was running the world at all times. Whereas now comes the promise of G-d that from now on the conduct of the world will be as if the world was ancient and eternal, that is, that everything is fixed according to order and as if everything behaves on its own without any leader and creator.
Therefore the seed and the harvest and the heat and the day and the night will not cease but will behave according to a pre-determined order as if there is never a permanent overseer who determines the order of the world as it will be, this is the depth of the intention of G-d in the promise For all the days of the earth, it will not cease. Therefore it was derived by our Sages that an idolator who keeps Shabbos is liable to the death penalty. As I have explained a number of times that while the descendants of Noach (bnei noach) were commanded to keep 7 mitzvos as well as the belief in one G-d, they were not commanded to believe that the world had been created. In fact it is actually prohibited for a person to look what preceded the world and what comes after [Chagiga (16a)]. Regarding Jews, since they received the Torah at Sinai which clearly states that G-d created the world from nothing, we are required to believe that the world is not eternal but that it had been created by G-d. And Shabbos is the sign that G-d established for the Jews to remember "For in six days God made the heavens and the earth, and on the seventh day He rested" Therefore the non Jew who were not commanded to believe in the creation of the world were are also not commanded to observe Shabbos. Therefore a goy who keeps Shabbos is liable to the death penalty. Because if he observes Shabbos, he may come under the prohibition of looking forward and backward. Any thing they are warned against not doing, they are liable to the death penalty . Consequently G-d reveals in this verse that His manner of running the World after the Flood will be different than what it was before in that it will now seem that the world is eternal and not created. In other words after the Flood it will appear that the World runs by itself in a natural manner. It is no longer apparent that this needs to be investigated or that there are doubts about this and therefore it is obvious why our Sages said that a goy who keeps Shabbos is liable to the death penalty