Here I begin to render into English the Kitzur Shulchan Aruch at the beginning of the Laws of Shabbos: 72:1.
The holy Shabbos is the great sign and covenant that HKBH gave us, so that we may know that He fashioned heaven, earth, and all that they contain in six days and rested on the seventh day. This is, indeed, the foundation of our faith. Razal (our sages) teach us that Shabbos is as important as the entirety of all the mitzvos; and that one who properly observes the Shabbos is equal in standing to one who fulfills the entirety of the Torah. Moreover, someone who desecrates the Shabbos is the same as someone who denies the entire Torah. The verse in Ezra supports this when it says: And You descended on Mount Sinai, and You gave Your people Torah and mitzvos. You also told them about Your holy Shabbos.
72:2 Anyone who publically desecrates the Shabbos is accounted a non-Jew in all respects. If he should touch wine, it is rendered prohibited. The bread he bakes is considered bread baked by a non-Jew. So too for a dish that he cooks:it is as if a non-Jew had cooked it. (For more, see below at 72:38.) By publically is meant in the presence of ten people. It is not, however, necessary that they should actually observe him in the commission of his act. It is sufficient if they are aware that he has committed it.
72:3 This is why the prophet offers commendation and says: Praised is the person who will do this, and the man who holds steadfastly to it – the one who will guard the Shabbos and desist from flouting it... The prophet says as well that someone who keeps the Shabbos as it is commanded to be kept and, also, honors it and makes it enjoyable to the best of his ability – such a person merits to be rewarded not only in the World to Come but also in This World.