Charles Ellicott Commentary Joshua 18:5-10

"And they shall divide it into seven portions: Judah shall abide in his border on the south, and the house of Joseph shall abide in their border on the north. And ye shall describe the land into seven portions, and bring [the description] hither to me; and I will cast lots for you here before Jehovah our God. For the Levites have no portion among you; for the priesthood of Jehovah is their inheritance: and Gad and Reuben and the half-tribe of Manasseh have received their inheritance beyond the Jordan eastward, which Moses the servant of Jehovah gave them. And the men arose, and went: and Joshua charged them that went to describe the land, saying, Go and walk through the land, and describe it, and come again to me; and I will cast lots for you here before Jehovah in Shiloh. And the men went and passed through the land, and described it by cities into seven portions in a book; and they came to Joshua unto the camp at Shiloh. And Joshua cast lots for them in Shiloh before Jehovah: and there Joshua divided the land unto the children of Israel according to their divisions." — Joshua 18:5-10 (ASV)

They shall divide it into seven parts. —The several tribes were not permitted to choose their own portions. In Numbers 26:54-55, we read: To many you shall give the more inheritance, and to few you shall give the less inheritance... notwithstanding the land shall be divided by lot. These words imply that there must be unequal portions of territory for larger and smaller tribes, but that the particular position of each tribe must be settled by the lot, of which the whole disposing is of the Lord. We are not told how this rule was carried out in the case of Judah, Ephraim, and Manasseh, who received their inheritance first.

Possibly a sufficient extent of territory was surveyed at first to provide three large allotments. The three tribes might then cast lots, first between Judah and Joseph for the northern or southern portions, and then between Ephraim and Manasseh for the two sections of the northern territory. This would carry out the instructions of Numbers 26:0. But see above (Joshua 15:1).