1)
Whom does this address?
1.
Rashi: It addresses Mo'av.
2.
Malbim: Now it returns to Edom.
2)
Why does it say "Mivtzar Misgav Chomosecha"?
1.
Radak: It is Samuch to Samuch, like "Mispar Mifkad ha'Am" (Shmuel II, 24:9) and similar verses.
2.
Malbim: Batzrah, the strong city of Edom - do not be haughty that your walls protect you.
3)
Why does it say "Ad Afar"?
1.
Radak: It will not rise again.
2.
Malbim: Hashem will lower [your walls] until the ground below. After, you will reach until the ground, and resemble earth (26:5). There will be no mark at all if there was a fortress and wall here.