And a field, a suburb of their cities, is not sold; for a possession age-during it is to them.

But the land on the outskirts of their towns may not be exchanged for money, for it is their property for ever.

But the fields of the open land about their cities may not be sold; for that is their perpetual possession.

But let not their suburbs be sold, for it is an everlasting possession.

Ager autem suburbii urbium eorum non vendetur, quia possessio perpetua est illis.

But the field of the (q) suburbs of their cities may not be sold; for it [is] their perpetual possession.
(q) Where the Levites kept their cattle.

But the field of the suburbs of their cities may not be sold,.... The suburbs to the cities of the Levites reached two thousand cubits on every side of their cities, Numbers 35:5; in which they had fields to keep their cattle in, and these belonged to them in common; every Levite had not a particular field to himself as his own property, and which is the reason why it might not be sold, nor might they agree together to sell it, for then they would have nothing to keep their cattle in: the Jewish writers generally understand this of changing their fields, suburbs, and cities: hence they say, in the Misnah, they do not make a field a suburb, nor a suburb a field, nor a suburb a city, nor a city a suburb; upon which Maimonides (o) says, all agree that the Levites may not change a city, or suburb, or field which are theirs, because of what is said, Leviticus 25:34; and the wise men, of blessed memory, say, the meaning of it is, it shall not be changed, for they do not change anything from what it was before:
for it is their perpetual possession: and therefore never to be alienated from them, or be sold to another, or changed and put to another use; such care was taken of the ministers of the sanctuary, and of their maintenance and support, under the former dispensation; and suggests that they should continue in their stations without any alteration, as ministers of the Gospel should, who ought to give up themselves to the ministry of the word, and prayer, and not entangle themselves with the affairs of life.
(o) In Misn. Eracin, c. 9. sect. 8.

The field of the pasture-ground of the Levitical towns was not to be sold. Beside the houses, the Levites were also to receive מגרשׁ pasturage for their flocks (from גּרשׁ to drive, to drive out the cattle) round about these cities (Numbers 35:2-3). These meadows were not to be saleable, and not even to be let till the year of jubilee; because, if they were sold, the Levites would have nothing left upon which to feed their cattle.
Leviticus 25:35-55
The second effect of the jubilee year, viz., the return of an Israelite, who had become a slave, to liberty and to his family, is also introduced with an exhortation to support an impoverished brother (Leviticus 25:35-38), and preserve to him his personal freedom.

May not be sold - Not sold at all, partly, because it was of absolute necessity for them for the keeping of their cattle, and partly because these were no enclosures, but common fields, in which all the Levites that lived in such a city had an interest, and therefore no particular Levite could dispose of his part in it.