What is the role of observing Shabbat in ethics?
A person must keep himself from what disrupts the revelation of the Kedusha [holiness] of the Shabbat. The weekdays are the place of work, when one must exert to annul his will to receive, on which there were Tzimtzum [restriction] and concealment so as not to feel the existence of the Creator. One may believe that “The whole earth is full of His glory,” but he does not feel it due to the Tzimtzum that was done so as to avoid the bread of shame.
When one exerts over this and is rewarded with the aim to bestow, he begins to feel the Kedusha and is rewarded with the quality of Shabbat. Hence, on Shabbat we should observe the Shabbat, so the intruders, meaning the will to receive, do not come. Otherwise, the quality of Shabbat will promptly depart from him.