Comentario sobre Exodo 21:21

אך אם יום או יומים יעמד לא יקם NOTWITHSTANDING IF HE CONTINUE A DAY OR TWO, HE SHALL NOT BE AVENGED — If the master is free of the death penally in case of the servant remaining alive one day, is it not logical that he is free if he lives two days (what need is there for Scripture to add יומים)? But it adds it to show that the term יום is to be defined by יומים — “a day that is like two days”. And what kind of day is thereby meant? A period of twenty-four hours (a day which comprises a part of two separate days) (cf. Mekhilta d'Rabbi Yishmael 21:21:1).

כי כספו הוא, and it is up to him to discipline him. Sometimes a slave’s insubordination continues until the master is forced to administer a strong blow. We have read of such in Proverbs 17,11 ומלאך אכזרי ישלח בואך מרי יבקש רע, “an evil man seeks to rebel; therefore a cruel messenger will be dispatched against him.”

לא יקם כי בספו הוא, he will not be avenged for it was his own money. If he killed the slave unintentionally (in the accepted sense of the word), the master will have to be confined in a city of refuge on account of this. In this ruling there is no difference between putting to death of one's slave or some other human being. Exile is applicable only if one killed directly, in accordance with the definitions we outlined in verse 12. The Torah only needed to write in which respect the law of a master killing a slave is different from someone who kills a person who is not his slave.