The thirteen priestly cities (see the marginal references) were all in the tribes of Judah, Simeon, and Benjamin. Thus, as Calvin remarks, God so o…

Which the children of Aaron, [being] of the families of the Kohathites Who descending from Kohath, in the line of Aaron, …

By mixing the Levites with the other tribes, they were made to see that the eyes of all Israel were upon them, and therefore it was their concern t…