John Calvin Commentary Numbers 36:5

"And Moses commanded the children of Israel according to the word of Jehovah, saying, The tribe of the sons of Joseph speaketh right." — Numbers 36:5 (ASV)

And Moses commanded the children of Israel. The account given here is not identical to the previous one (that Moses referred the matter to God); yet the same thing is more briefly stated, namely, that Moses answered the people from the mouth of God, from which we infer that God was consulted by him. Moreover, God not only decides in favor of the children of Manasseh, but approves of their appeal, since they were contented with their allotment and claim for themselves what could not be alienated without violating the Divine decree.

From this particular occasion, a general law is established, that no woman to whom an inheritance had fallen was to marry outside her tribe, because she would defraud her own relatives of her marriage portion. In this way, however, free permission to marry was granted to women, provided they renounced their paternal inheritance.

The words, indeed, seem to have a wider application, that is, that no man should marry a wife except from his own kindred; but the meaning of the law is to be sought from the cause that led to its enactment. Moreover, there is no doubt that indiscriminate marriages are forbidden here, insofar as they confound the order of hereditary rights.