1)
Why does it specify marrying Bnos ha'Nochrim?
1.
Malbim: "Pen Tichros Bris l'Yoshev ha'Aretz...; v'Lakachta mi'Benosav l'Vanecha" (Shemos 34:15-16). Inheritance of the land and keeping it depend on this, like it says in Yehoshua 23:12-13.
2)
What will you bequeath?
1.
Rashi: The land to your sons, permanently.
