“And the assembly will bring him back to the city of his refuge…” (Bamidbar 35:25)
It is a positive commandment that the Beis Din of Klal Yisrael were commanded to exile an accidental murderer into a city of refuge, as it says “And the assembly will bring him back to the city of his refuge… and he will live there until the death of the High Priest!”. The murderer himself also must fulfil this commandment as it says “for he must live in the city of his refuge until the death of the High Priest!”.
Amongst the roots of this commandment are that the sin of murder is very severe as it destroys the world. It follows that even one who killed accidentally, since he was the instrument which caused this terrible thing. For this reason he must go into exile which is almost like death as in this exile he is separated from his family, friends and birthplace, and must live all his days with people whom he considers strangers. This commandment also achieves that by doing this he will be saved from the “redeemer of the blood”, that he can no longer kill him when he has not committed a crime. Another reason is that the relatives of the person who was killed will not see the murderer regularly, and all the ways of the Torah are pleasant.
Amongst the laws of this commandment are that a Jew who kills a Jew, a slave or a non-Jew who has undertaken to fulfil the seven Noachide commandments, must go into exile. The same applies to a slave who kills one of the above.
This commandment applies when Klal Yisrael are in their own land, with a High Court of seventy-one judges sitting in their designated place in Yerushalayim to deal with the death penalty, (when this High Court exists, that delegates the power to every court in every town to judge cases of the death penalty and exile). If the beis din does not send a man into exile they have transgressed this commandment and their punishment is very great, as this will cause bloodshed.