Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
Joshua Chapter 21
A list of the Levitical cities, varying in some particulars from that given in this chapter, is also, given in 1 Chr. 6:54-81.
Thirteen cities - This number is said to be too great for the single family of Aaron. But it appears 1 Chr. 24 that the two surviving sons of Aaron, Eleazar and Ithamar, had together 24 sons, the heads of the priestly families. Since Aaron was 123 years old when he died Num 33:39, his sons' grandchildren and great grandchildren were no doubt living in the elapsing years of Joshua's course, and had to he provided with dwellings. They might altogether number several thousands. The "cities" of Canaan were for the most part small; as is manifest from the astonishing number of them in proportion to the area of the land, more particularly in the south, where the portion of the priests was situated. The priests or Levites would not occupy the whole of the dwellings in any city, nor all its "fields," nor necessarily and always all its "villages" (compare Jos 21:12). Non-Levites, to whom the cultivation of their land, and other secular concerns, were entrusted, no doubt resided in the Levitical cities or their precincts. It appears, further, that several of the cities here enumerated were only wrested from the Canaanites at a later date.
The non-priestly Kohathites had been diminished by the destruction of Korah and his company Num. 16. On comparing Num 26:57 following with Num 3:27 ff, two of the families of the Kohathites seem to have disappeared altogether. Hence, it is not surprising that the rest of the Kohathites were sufficiently accommodated in ten cities.
The thirteen priestly cities (see the marginal references) were all in the tribes of Judah, Simeon, and Benjamin. Thus, as Calvin remarks, God so overruled it that the priestly families were placed upon the spot which He had determined before hand to choose as the site of His temple.
Of the cities of the non-priestly Kohathites, for Kibzaim we find Jokmeam in Ch1 6:68. This is perhaps another name for the same place, since both names may be derived from roots having a similar meaning; and for Gath-rimmon in Ch1 6:70, Bileam is given, and probably correctly; Gath-rimmon having apparently been repeated inadvertently from the preceding verse. Bileam is but another form of Ibleam Jos 17:11.
Compare Jos 19:18, etc. Of the cities of the Gershonites, for Beesh-terah read (Beeshterah.) The name is a contraction of Beth-Ashterah ("house of Ashterah") and the city is undoubtedly the Ashtaroth or Astaroth of Og Jos 12:4; Deu 1:4; Ch1 6:71.
Merarite cities. Some of these places are not found in the list of Zebulonite cities in Jos 19:10-16. The text is considered corrupt.
After this verse, the Septuagint introduces a passage (in part a repetition from Jos 19:49-50), recording the grant of a special inheritance to Joshua, and also that he buried at Timnath-serah the flint-knives with which he had circumcised (Jos 5:2 note) the people after the passage of Jordan. The latter statement, which has the authority of the Septuagint only, is a Jewish legend of early date.
There is no real inconsistency between the declarations of these verses and the fact that the Israelites had not as yet possessed themselves of all the cities allotted to the various tribes Judg. 1:21-36 - nor did at any time, subdue the whole extent of country promised to them Num 34:1-12. God had fulfilled all His part of the covenant. It was no part of His purpose that the native population should be annihilated suddenly Deu 7:22; but they were delivered into the hand of Israel, and their complete dispossession could have been effected at any time by that divine aid which was never wanting when sought. At the time referred to in the text, the Canaanites were discouraged, broken in strength, holding fast in isolated spots only up and down the land in the very midst of the tribes of God's people. The conquest of Canaan was already "ex parte Dei" a perfect work; just as in the New Testament the triumph of the individual Christian and of the Christian Church in their warfare is often spoken of as accomplished in view of the divine will that it should be so, and of divine grace that it may be so. It was therefore, only the inertness and pusillanimity of the Israelites which prevented the completion of the conquest when the allotment of Canaan was made by Joshua; as it was their subsequent backslidings which caused God to turn the tide of victory against them and even to cast them out of the land promised to their forefathers and actually won in the campaigns of Joshua. See the introduction to the Book of Joshua.