ליקוטי הלכות: הלכות שבת, הלכה ז:יא
ושמרו בני ישראל את השבת -
And Bnei Yisrael will keep the Shabbos (שמות לא:טז) -
Even though the holiness of Shabbos is inherently permanent as determined by Hashem Yisborach, and there is nothing that can detract from its holiness in anyway, the Jews must accept the Shabbos and keep it, as it's written, "And Bnei Yisrael will keep the Shabbos, etc". The holiness of Shabbos isn't drawn into the world except through the Jews as it's written, "And Hashem didn't give it to the nations of the lands etc." The sages say in Bereshis Rabba that Shabbos approached The Holy One Blessed is He, and said, "You gave every [day] it's pair [and not me]! And Hashem responded to the Shabbos, "Knesses Yisrael is your pair." Therefore, the holiness of Shabbos depends on every single Jew. Therefore, the act of saving a life defers Shabbos, because it's better to desecrate one Shabbos than to desecrate many Shabbosim. When even one Jewish soul is removed from this world it is considered a desecration of Shabbos. This desecration is an aspect of the removal and death of holiness as is noted in the words of Rabbeinu z"l, "When a single Jew, who is a part of knesses Yisrael, which is the pair of Shabbos, dies and is removed from the world, it is considered a desecration of Shabbos." And, thus it's better to save a life and desecrate one Shabbos, than [have a Jew die and] desecrate many Shabbosim.
I gather that one of the reasons why the desecration continues is because there's no way a person can rectify the
chilul Shabbos in the future, because, well...he's dead! Rabbeinu writes in רעז that the
tikkun for desecrating Shabbos is through
achila for the sake of Shabbos. A dead person cannot eat during any forthcoming Shabbos, and therefore it can't be rectified atleast in this world. But what about
ochel ruchani? Could that rectify the desecration of Shabbos caused by a Jew's death? And, who actually desecrates that particular Shabbos when the Jewish soul departs this world? Is it the individual or all of Knesses Yisrael?
Regardless, the beauty of Reb Nosson's words lies in the fact that he stresses how important it is that the Jews recieve Shabbos. If the Jews were to foresake Shabbos, she would not only have no pair, but her intrinsic holiness would be neglected and ignored completely, because "Hashem didn't give it to the other nations." Shmiras Shabbos is solely up to the Jewish people, and kabbalas Shabbos depends on every single Jew.
