Musar zu Schemot 21:21

I have explained the significance of the rule of a slave dying more than twenty four hours after having been struck by his master (Exodus 21,21), in my commentary on פרשת יתרו. The first of the Ten Commandments, אנכי, which is one of the positive commandments, includes the essence of all positive commandments, whereas the second of the Ten Commandments, לא יהיה, not to have other deities, contains the essence of all the other negative commandments. Our sages have said that the 365 negative commandments correspond to the 365 days in the solar year (Makkot 23). When the Torah says יום in our verse, it refers to all 365 days of this temporal year. A Gentile slave is obligated by Jewish law to observe all the negative commandments, whereas he only has to observe those positive commandments that Jewish women also have to observe. He is exempt from the performance of commandments which are linked to a specific time frame i.e. a certain part of the day. It follows that his sanctity is restricted to "a (full) day one," i.e. when he performs all the negative commandments. This is the deeper meaning of the Torah saying "if he survives a day or two." יום או יומים, means a "day that includes all days, a period of not less than twenty four consecutive hours."