In this final chapter of Numbers, the daughters of Zelophehad are instructed to marry within their tribe to maintain their tribe's inheritance.
This chapter continues on the theme of allocating the promised land. Chapter 34 dealt with the boundaries and distribution of the land, chapter 35 dealt with the Levitical cities (their allotment within the land) and this chapter deals with a technicality resulting from the earlier pleas of the daughters of Zelophehad concerning their father's inheritance (I commentated this in detail in Num 27). I would recommend reading my commentary on Num 27 because in it, I discuss the concept of inheritance, how that was understood in Israelite society, and how it relates to Zelophehad's daughters. The basic idea is that with no sons, the property of Zelophehad goes to his daughters to help carry on his estate and his "name" amongst his family. One of the principles of inheritance is that the property of the wife is given to her husband, and this chapter is largely how we figure that out.
The leaders of Manasseh are complaining that if Zelophehad's daughters marry outside of Manasseh, then Zelophehad's property will be permanently given to that other tribe. The tribal inheritances are meant to be permanent (you did read my commentary on Num 27 right?), so transferring property from one tribe to another breaks that permanence.
Normally this isn't a problem, since normally sons inherit the property of their fathers. As a male, the property remains within their own family and therefore the tribal boundaries are maintained even if they marry women from other tribes (we can reason from this chapter that this was normally allowed). This only becomes a problem when a woman inherit her father's land and ergo pass it on to her husband.
Moses responds by agreeing to close this loophole. Any woman who inherits property from her father must marry within her father's tribe. This serves the dual role of preserving her father's name amongst his brothers (as per Num 27) and preserving the land within the larger tribe, consistent with the apportionment of Num 34.
This is really only a technicality, but it teaches us a lot about how the Israelites treated inheritances between women and men. In fact, this chapter is the basis of a lot of what I said in my commentary on Num 27, since cross-referencing these two chapters with Num 34 gives a much more complete picture than just reading Num 27 alone.
And with that, we conclude the book of Numbers. The Israelites are now encamped in the plains of Moab adjacent to the Jordan river, opposite Jericho. They are preparing for the invasion with Moses detailing many laws related to the land, which is uniquely relevant given their impending invasion. However, we are not yet ready to conquer the promised land. Next we are going to read the book of Deuteronomy as Moses just keeps talking. I kid you not: 34 chapters of Moses talking virtually non-stop. I'm not going to steal my own thunder and give the introduction to Deuteronomy here, however: onward!