Rambam - 1 Chapter a Day

Sefer HaMitzvot (Positive Commandment 182) and Sefer HaChinuch (Mitzvah 520) regard this as one of the Torah’s 613 commandments.

The verse cited as a proof-text continues, emphasizing that these cities shall be “in your land, which God your Lord is giving you as an inheritance.” The Sifre Zuta interprets this to be an exclusion, teaching that such cities should not be set aside in the diaspora.
Nevertheless, if a person kills unintentionally in the diaspora, he should flee to one of the cities of refuge in Eretz Yisrael (Kessef Mishneh, interpreting the Sifre).

Although only two and a half tribes lived in TransJordan and nine and a half lived in the land of Canaan, the same number of cities were set aside in both areas. Makkot 9b explains that murderers are commonly found in Gilead (one of the regions in TransJordan).
[Kin’at Eliyahu offers a different explanation, noting that all the 42 cities of the Levites that also served as cities of refuge were located in the land of Canaan, thus tipping the ratio considerably in favor of the land of Canaan.]

For his actions were of no immediate consequence.

Kin’at Eliyahu questions the place of this statement in the Rambam’s Mishneh Torah. The Mishneh Torah is a book of halachah - Torah law - and not a text of ethical teachings. Why then does it mention this point? He explains that this teaching - to fulfill a mitzvah whenever one can - is also a halachah, a point of Torah law.
In that vein, see the Rambam’s Commentary on the Mishnah (Avot 4:2), which cites this deed performed by Moses as a “shining example” of the teaching “Run to [perform even] an easy mitzvah.” The Rambam concludes there: “If Moses our teacher... the most perfect of all men, endeavored to add the fulfillment of half a mitzvah to his attainments... needless to say, this course of action should be followed by those who have tainted their souls.”

See also Hilchot Melachim 11:2. The Rambam cites the commandment to establish three new cities of refuge as a proof that there will be an Era of the Redemption. For “the Holy One, blessed be He, did not give this command in vain.”
The Rambam’s intent is that since the mitzvah of setting aside the cities of refuge also includes setting aside these three cities, that mitzvah will certainly be fulfilled in all its particulars. For the mitzvot are absolute Godly truth, and they are intended to be fulfilled on the material plane. Thus, these cities will ultimately be set aside for the purpose stated in the Torah (Likkutei Sichot, Vol. XXXIV).
Likkutei Sichot (based on the teachings of the Ari zal) also questions why it will be necessary for there to be cities of refuge in the Era of the Redemption. In that era of perfect existence, there will be no unintentional killings, so why will we need cities of refuge?
Likkutei Sichot offers a resolution based on Yoma 80a, which states that when Rabbi Yishmael (who lived after the Temple’s destruction) would inadvertently commit a transgression, he would write a note saying, “When the Temple is rebuilt, I will bring a succulent sin offering.” Similarly, the cities of refuge in the Era of the Redemption will be for those who killed unintentionally in the era of exile.

See Genesis 15:18-19. Our Sages interpret these three names to be referring to the nations of Edom, Moab and Ammon, whose lands extended to the south and west of Eretz Yisrael.

Makkot 9b exp1ains that these roads must be direct routes, without detours.

This is twice the width of an ordinary road.

This date was chosen because it was at the end of the conclusion of the rainy season, for it was in that season that the damage to the roads would take place. Also, that date was convenient because it coincided with the beginning of the collection of funds for the Temple treasury. These funds were used to repair these roads.

I.e., Chevron was the southernmost of the cities of refuge; Shechem, the center; and Kadesh, the northernmost (Joshua 20:7). The distance from Chevron to the southern border of Eretz Yisrael was the same as the distance from Chevron to Shechem. Similarly, it was the same distance from Shechem to Kadesh, and from Kadesh to the northern border of Eretz Yisrael (Makkot 9b).

For in such a situation, the blood redeemer may frequent the place (Rashi, Makkot 10a).

For in such a place it would be difficult for a newcomer to earn his livelihood.

I.e., these cities should be surrounded by other villages and towns. In this way, if several blood redeemers join together to do battle with the city of refuge, the neighboring villages will come to the aid of the city of refuge (ibid.).

These refer to snares for trapping animals. Nevertheless, they should not be set in a city of refuge, for trapping leads to hunting, which can lead to weapons being sold there. And thus, the blood redeemer may come and purchase a weapon and slay the killer.

Instead of being granted a portion of Eretz Yisrael as an ancestral heritage like the other tribes, the Levites were given 42 cities that were dispersed throughout the country.

The cities of refuge spoken about in the first clause of the verse.

For the land in these cities was specifically set aside for the unintentional killers.

I.e., both the cities of refuge and the cities of the Levites.

The term used by the Rambam has a specific meaning: the 2000 cubits from the city’s border, which serves as its Sabbath limits.

The Rambam’s ruling differs from that of most other commentators, who require the killer to climb unto the tree branches for them to serve as a haven for him.

This principle is found in several contexts. Since the tree itself is considered part of the city, its leaves are considered to be an extension of the city. See Hilchot Ma’aser Sheni 2:15.

This leniency of regarding the tree to be an extension of its leaves is unique, applying only with regard to a city of refuge. It is one more indication of the merciful nature of the Torah and its sages.