To the sons of Merari [were given] by lot, according to their families, out of the tribe of Reuben, and out of the tribe of Gad, and out of the tribe of Zebulun, twelve cities.
God had given the special privilege of being priests to Aaron and his sons as a gracious blessing. Normally the first-born son acted as priest of the family in the ancient Near East. This was one of the privileges of the birthright. Reuben had forfeited this, too, by his sin.