Why does it mention a lion?
Rashi: Also Nebuchadnetzar, who is called "Arye mi'Subecho" (Yirmeyah 4:7), will not be there.
What is "Peritz Chayos"?
Rashi: "Chazir mi'Ya'ar" (Tehilim 80:14). No Chayah is more violent than a wild pig.
Radak: It is the most radical Chayah, which breaches the fence of conduct of Chayos; it goes where people are found. Even it will not be found there; the redeemed will go there without fear.
What does "Ya'alenah" refer to?
Rashi: It will not ascend on that path. Derech can be masculine or feminine - "Es ha'Derech Yelchu 1 Vah" (Shemos 18:20 - feminine), "b'Derech Echad Yetz'u Elecha" (Devarim 28:7 - masculine).
Malbim: They will not be able to ascend on the path. The verse depicts as if the path is elevated so much that Chayos cannot ascend on it.
So Kli Paz cites Rashi. Our texts of Rashi say "Es ha'Derech Asher Yelchu Vah" (Nechemyah 9:12). Why would Rashi bring this verse, and not a verse from Chumash?! (PF)
What will not be found there?
Rashi: An evil Chayah. Radak - initially, it was a Midbar, a habitat of evil Chayos. Now, none will be found.
Why does it say "v'Halchu Ge'ulim"?
Malbim: There are three reasons why one cannot go in the Midbar (refer to 35:6:4:3). After they are annulled, the redeemed will go there without fear.