The Torah: A Modern Commentary (Plaut-Bamberger), Rev. Edition, p. 1117-8
Other Torah portions emphasize that the Levites were to be landless, while Num. 18 expressly provides for their support to compensate for their landlessness. Deuteronomy too speaks of them as people who need protection similiar to strangers, orphans, and widows. Yet the present section does make a land allotment to them.
Some scholars believe that the provisions in this chapter, which assign forty-eight towns west and east of the Jordan to the Levites, were never fully carried out, and that in effect the Levites were scattered among the tribes, without significant holdings of their own. But it has been shown that for a short time during the time of David and Solomon, Levitical towns played an important socio-political role, and that Levitical families lived in these cities at some time. Among the designated Levitical cities were six that served as "cities of refuge" (35:9-34), an arrangement reflection ancient concepts of law and justice....
(2) [If one] intended to kill an animal and killed a person; [or intended to kill] a non-Jew and killed a Jew; [or intended to kill] a fetus that was not viable and killed a viable fetus, he is exempt. [If he] intended to strike another on his loins, without enough [strength] to kill him [by striking] his loins, and the blow hit him on his heart with enough strength to kill him, and he died, he is exempt. [If he] intended to strike another on his heart, with enough strength to kill him on his heart, and the blow hit him on his loins, without enough strength to kill him on his loins, and he died, he is exempt. [If he] intended to strike an adult, without enough strength to kill an adult, and the blow landed on a minor, with enough strength to kill a minor, and he died, he is exempt. [If he] intended to strike a minor, with enough strength to kill a minor, and the blow landed on an adult, without enough strength to kill an adult, and he died, he is exempt. However, [if he] intended to strike another on his loins with enough strength to kill him on his loins, and the blow landed on his heart, and he died, he is liable. [Similarly, if he] intended to strike an adult, with enough strength to kill an adult, and the blow landed on a minor, and he died, he is liable. Rabbi Shimon says, even [if he] intended to kill this one, and he killed that one, he is exempt.
(2) One who throws a rock into the public domain and it kills someone, he is exiled. Rabbi Eliezer ben Yaakov says: if the person stuck his head into the public domain only after the stone left his [the killer's] hand, he is exempt. If he threw the stone into his courtyard and it killed, if the victim had permission to be there, he is exiled, but if he did not have permission, he is not exiled, as it says, "If he comes upon his fellow in the woods..." (Deuteronomy 19:5). Just as the woods is open to both the victim and the perpetrator to enter there, this excludes a privately owned courtyard where both the victim (and the perpetrator) does not have permission to be there. Aba Shaul says: Just as chopping wood is optional, [so too one is only exiled for optional activities] this excludes a father beating his son, a teacher disciplining his student, and the messenger of the courts.
Rabbenu Bachya on Numbers 35:11:2
“and to such a city a murderer who killed a person unintentionally shall flee.”
Such a person is not guilty of the death penalty seeing he did not intend to kill his victim. This law demonstrates that the heart of the person is the prime driving force of man’s activities. This principle applies to the performance of all the commandments as well as to the commission of any sins. Exile is the penalty decreed here seeing that the man’s heart was not associated with his action. The death penalty never applies unless body and heart had committed the sin in question in tandem, in agreement with each other. The body contributes the relevant movement, the heart the relevant intention. Seeing in the example mentioned there was no such co-ordination between body and mind, the guilty party only has to be exiled. By the same token, if a person performed a commandment, in accordance with all its details but his heart was not involved, i.e. he did not mean to perform a commandment by doing what he did, he will not receive a reward for his deed.
Numbers Rabbah 23:13
Once Moshe stood and the Holy Blessed One told him, "Provide yourselves with cities...", Moshe said "Master of the Universe, this one killed by accident in the south or the north; how will he know where the city of refuge is, that he may flee to it?" God replied, "'Set for yourselves the path... [i.e. to the cities of refuge]' (Deuteronomy 19:3), orient for yourselves the path so that you will not be mistaken and find the blood avenger and he will kill you "and there will be for him no death penalty" (Deuteronomy 19:6)." He [Moshe] said again, "How?" He [God] said to him, set up for yourselves signs [istlayot] pointing to the cities of refuge, that they will know where to travel. And on every sign write "Killer to the city of refuge", as it says "prepare for yourselves the way". Thus said David, "Good and upright is the Lord, therefore He shows sinners the way." If for killers He makes a path and a road for them to flee by and be saved, all the more so for righteous!
Makkot 10a
With regard to these cities of refuge, one does not establish them in small settlements or in large cities; rather, one establishes them in intermediate-sized towns. And one establishes them only in a place where water is available, and if there is no water available there, as there is no spring accessible from the city, one brings them water by digging a canal. And one establishes them only in a place where there are markets, and one establishes them only in a populated place, where there are many people who regularly frequent the town. If the population of the surrounding areas diminishes, one adds to it. If the number of residents in the city of refuge itself diminishes, one brings new residents to the city, among them priests, Levites, and Israelites. The baraita continues: And one may not sell weapons or hunting tools in the cities of refuge, to prevent the blood redeemer from gaining access to means that he could exploit to kill the unintentional murderer who fled to the city of refuge; this is the statement of Rabbi Neḥemya. And the Rabbis permit selling weapons and hunting tools. And Rabbi Neḥemya and the Rabbis agree that one may not spread nets in the cities of refuge, nor may they braid [mafshilin] ropes in those cities, so that the foot of the blood redeemer will not be found there. If the blood redeemer were to enter the city of refuge to purchase nets or ropes, he is apt to encounter the murderer and kill him. Rabbi Yitzḥak says: What is the verse from which these matters are derived? It is written: “And he shall flee to one of these cities and live” (Deuteronomy 4:42), meaning: Perform some actions for the unintentional murderer so that life in the city of refuge will be conducive to living for him. All these steps are taken to facilitate that objective.
Makkot 11a
"He must remain in his city of refuge until the death of the high priest" (Num. 35:28). For that reason, mothers of high priests used to provide food and clothing for manslayers, so that they should not pray for their sons' death.
The Torah: A Moden Commentary (Plaut-Bamberger), Rev. Edition p. 1130-1.
The institution of sanctuary had three purposes. It was a protective measure, to give everyone the opportunity to let passions cool.... It served further as a punishment for the accidental killer, because exile constituted a form of social death. The third and in some ways most important purpose was to contain and isolate the sin that had been commited, for killing was understood to contaminate the community.... The slaying of a human being, though it occured without evil intent, was a moral injury to the total community.
Chasidic- Ma'yanah shel Torah, Vol. IV, p.155, quoting Apter Rebbe
There were six cities of refuge and altogether forty-eight Levitical cities. Tis is akin to the Sh'ma as recited during prayer: the six Hebrew words of the sentance "Hear, O Israel" (Deut 6:4; traditionally recited with the intent of of focussing one's attention on what ultimately matters), and the forty-eight words of the paragraph "You shall love the Eternal your God..." that follows (Deut 6:5-9); traditionally recited to oneself, as a meditation). Just as the ancients could find succor in the Levitical cities when they had sinned, so today one may find surcease in "the city of Sh'ma."