We are up to Maseches Makkos, chapter 2, mishnah 4. The mishnah comes to clarify where an accidental killer goes into exile: to what place does he flee, and to which cities must he turn?
The words of the mishnah:
"L'heichan golin? L'arei miklat" - one who kills accidentally goes into exile to the cities of refuge.
"L'shalosh she'be'ever haYarden v'lishalosh she'b'Eretz Canaan" - three cities are located on the eastern side of the Jordan River, and three are located in the land of Canaan.
"Shene'emar: 'Es shalosh he'arim titnu me'ever laYarden v'es shalosh he'arim titnu b'Eretz Canaan'" - the verse in Bamidbar is the source for this division: three cities on the eastern side of the Jordan, and three in the land of Canaan.
The condition for providing refuge - all six together:
"Ad shelo nivcharu shalosh she'b'Eretz Yisrael, lo hayu shalosh she'be'ever haYarden koltos" - the three cities on the eastern side of the Jordan were already set aside by Moshe Rabbeinu during his lifetime, before the entry into the land of Canaan, and even so they did not function as cities of refuge until the additional three cities in the land of Israel were set aside.
"Shene'emar: 'Sheish arei miklat tihyenah' - ad sheyihyu sheish shetihyenah koltos k'achas" - the verse teaches that all six cities function as a single system. As long as all six cities do not exist and operate together, none of them provides refuge.
The cities of the Levi'im:
In addition to the six cities of refuge, the forty two cities of the Levi'im also serve as places of refuge, making a total of forty eight cities. Nevertheless, there is a halachic difference between the six cities of refuge and the forty two cities of the Levi'im in two respects:
The intent of the one who enters: the cities of refuge take in the accidental killer whether he entered them with the intention that they serve as his shelter or not. The cities of the Levi'im, by contrast, take him in only when his intention in going there was for refuge.
Rent: an accidental killer who lives in one of the six cities of refuge is not required to pay rent, whereas one who lives in one of the cities of the Levi'im is obligated to pay rent.
In summary: in this mishnah we learned that one who kills accidentally goes into exile to the cities of refuge - three on the eastern side of the Jordan and three in the land of Canaan; that even though the cities across the Jordan were set aside by Moshe Rabbeinu, they do not provide refuge until all six cities provide refuge together; and that the cities of the Levi'im join the count of cities of refuge to bring it to forty eight, but they differ from the cities of refuge regarding the law of intent and the obligation to pay rent.