Seeing as the Torah goes on to define the borders of Eretz Yisrael, why does it see fit to insert the words "Kol ha'Makom asher Tidroch Kaf Ragl'chem ... "?
Rashi (in Yehoshua, 1:3): It means that after you conquer all of Eretz Yisrael, any place that you capture in Chutz la'Aretz, will become sanctified and belong to you.
Rashbam: 'Wherever you fight the seven nations, it will become yours'.
Ramban: These are two promises: a. Any land that you conquer in the lands of Shin'ar (Bavel) or Ashur or anywhere else will belong to you 1 and b. The specified land will be your borders - and you are obligated to conquer it and to destroy the nations who live there. 2
What is the significance of "Midbar", "N'har P'ras" and "Yam ha'Acharon"?
Rashi (in Yehoshua, 1:4): With reference to Midbar Tzin, which was situated on the south-eastern tip of Eretz Cana'an, where Yisrael were currently encamped, and from where they entered Cana'an - See Bamidbar 20:16. (This requires investigation. That verse says that we were on the border of Edom, and we asked to pass through to get to Eretz Yisrael! Also, Yisrael passed by Edom and Mo'av, and conquered Sichon and Og, and from there entered Eretz Yisrael!
What is "Levanon" referring to?
Targum Onkelos: It refers to Lebanon. 1
Targum Yonasan: It refers to the mountain of (on which was built) the Beis-Hamikdash. 2
Even though in Devarim 3:25, Targum Onkelos interprets "Levanon" in the context there as 'the Beis-Hamikdash'.
Rashi (3:25) said so, but there Moshe listed what he wanted to see in Eretz Yisrael. Rashi could hold like Targum Onkelos that here, discussing the borders of Eretz Yisrael, it refers to Lebanon. (PF)
What is the "Yam ha'Acharon"?