III. That there were thirteen cities, and those some of the best, appointed for the priests, the sons of Aaron, v. 19. Aaron left but two sons, Eleazar and Ithamar, yet his family was now so much increased, and it was foreseen that it would in process of time grow so numerous, as to replenish all these cities, though a considerable number must of necessity be resident wherever the ark and the altar were. We read in both Testaments of such numbers of priests that we may suppose none of all the families of Israel that came out of Egypt increased afterwards so much as that of Aaron did; and the promise afterwards to the house of Aaron is, God shall increase you more and more, you and your children, Ps. cxv. 12, 14. He will raise up a seed to serve him.