1)
What is the significance of the fact that Hor ha'Har was on the border of Eretz Edom?
1.
Rashi (citing Bamidbar Rabah): It teaches us that they lost Aharon because they made efforts to come close to Eisav ha'Rasha. 1
2.
Oznayim la'Torah (in Mas;ei, 33:37: It distinguishes it from the Hor ha'Har on the northwestern tip of Eretz Yisrael. 2
1
Rashi: In the same way as the Navi said to King Yehoshafat (in Divrei ha'Yamim 2, 20:37) "Because you aligned yourself with Achazyahu (the wicked king of Yisrael), Hashem has breached your undertakings".
2
Recorded in Mas'ei, 34:7. See also Oznayim la'Torah (Ibid.)