What is the meaning of "Yesusum"?
Rashi: They will rejoice over them. It is as if it says Yesusu Mehen. This is like "Banai Yetza'uni" (Yirmeyah 10:20) - Yatz'u Mimeni.
Radak #1: The final Mem is in place of a Nun that appears often in future tense - e.g. Yishme'un.
Radak #2: The final Mem is in place of Bam or Imam. The Midbar in which these Chayos dwelled, they will rejoice in them when they go to dwell in Edom.
What are "Midbar v'Tziyah"?
Rashi: Yerushalayim is called Tziyah, and Tziyon is called Midbar. They will rejoice over the downfall of the Giborim of Sa'ir.
Radak #1: They are where these Chayos used to dwell.
Radak #2: Eretz Yisrael was like a Midbar from when Yisrael were exiled from it. It will rejoice at the Churban of Edom, for when one [of Yisrael and Edom] is destroyed, the other is settled.
Malbim: A Midbar is not proper to be seeded due to itself (the land). Tziyah is not proper to be seeded due to the heat of the sun above. Aravah was proper to be seeded, but it was ruined due to thorns and wild animals. Chutz la'Aretz is called Midbar v'Tziyah because it is not proper for light. It itself is like a Midbar, and also due to its root in Shamayim above.
Why does it mention Sason and Gil?
Malbim: Sason are external acts to show Simchah, e.g. playing drums, harp and dancing. Simchah and Gil are of the Nefesh. Simchah is constant joy. Gil is over a new matter, e.g. finding something or good tidings. Chutz la'Aretz, which is not proper for Simchah of the Nefesh, will have external Simchah from the fall of Edom.
Which Aravah is discussed?
Rashi: It is the Aravah (desert) of Yerushalayim.
Malbim: This refers to Eretz Yisrael. It is proper for Divine light due to itself, and due to its source above. However, thorns grew in it, i.e. bad deeds that were Metamei it. It will have new internal Gil, for after being full of thorns it will sprout like a rose.
What is "Chavatzeles"?
Radak: It is a rose, which blossoms and gives scent.
