Numbers 36:5

Here is, I. The matter settled by express order from God between the daughters of Zelophehad and the rest of the tribe of Manasseh. The petition is assented to, and care taken to prevent the inconvenience feared: The tribe of the sons of Joseph hath said well, Num 36:5. Thus those that consult the oracles of God concerning the making of their heavenly inheritance sure shall not only be directed what to do, but their enquiries shall be graciously accepted, and they shall have not only their well done, but their well said, good and faithful servant. Now the matter is thus accommodated: these heiresses must be obliged to marry, not only within their own tribe of Manasseh, but within the particular family of the Hepherites, to which they did belong. 1. They are not determined to any particular persons; there was choice enough in the family of their father: Let them marry to whom they think best. As children must preserve the authority of their parents, and not marry against their minds, so parents must consult the affections of their children in disposing of them, and not compel them to marry such as they cannot love. Forced marriages are not likely to prove blessings. 2. Yet they are confined to their own relations, that their inheritance may not go to another family.

— Matthew Henry's Concise Commentary (public domain)

Moses commanded the children of Israel according to the word of the Lord--The plea appeared just and reasonable; and, accordingly an enactment was made by which the daughters of Zelophehad, while left to the free choice of their husbands, were restricted to marry not only within their own tribe, but within the family of their father's tribe--that is, one of their cousins. This restriction, however, was imposed only on those who were heiresses. The law was not applicable to daughters in different circumstances (Ch1 23:22) --for they might marry into another tribe; but if they did so, they were liable to forfeit their patrimonial inheritance, which, on the death of their father or brothers, went to the nearest of the family kinsmen. Here was an instance of progressive legislation (see also Exo 18:27) in Israel, the enactments made being suggested by circumstances. But it is deserving of special notice that those additions to, or modifications of, the law were confined to civil affairs; while the slightest change was inadmissible in the laws relating to worship or the maintenance of religion.

— Jamieson-Fausset-Brown Commentary (public domain)