Commentary for Numbers 36:4

ואם יהיה היבל may mean AND IF THERE WILL BE THE JUBILEE — From this R. Judah said: The observance of the Jubilee will cease at some time or other (Sifra, Vayikra Dibbura d'Nedavah, Section 13 1 on Leviticus 2:14).

ואם יהיה היובל...יגרע נחלתן, even in the event that we will not now conquer the whole land, as predicted in Exodus 23,30 that the land would be conquered in stages, progressively, so that each tribe would have to conquer the area it laid claim to, a person who had sold his share or potential share could not claim exemption form the war of conquest seeing that the land he had sold would be restored to him in the Jubilee year. In any event it would remain part of his tribe’s ancestral heritage. However, the share given to the daughters of Tzelofchod which would not be restored to their tribe in the Jubilee year, would furnish an excuse to members of their tribe not to bother to fight for that piece of land, and they would allow the present owners to remain there. At any rate, the argument of the family of Machir of Menashe was that the most recent legislation could result in the whole principle of sharing out the land by lottery being partially aborted.

ואם יהיה היובל לבני ישראל, “and when the Jubilee year will arrive for the Children of Israel, etc.” These people argued that if the daughters of Tzelofchod were to marry someone outside their tribe, the heritage they had been given would then pass over to their husbands and as a result would never revert to their tribe even in the Jubilee year. The result would be an increase of ancestral land of some other tribe at the expense of the tribe of Menashe. The legal reason was that inherited property is not subject to the Yovel legislation.