Why should you lift your eyes?
Malbim: Refer to 51:6:2:6.
What is the meaning of "Shamayim k'Ashan Nimlachu"?
Rashi #1: The officers of the legions of Nochrim in Shamayim will wither. This is like "Sechavos u'Vloyei Melachim" (Yirmeyah 38:11) - a destroyed garment.
Rashi #2: [Sarei Nochrim in Shamayim] were perturbed. This is like Melachei ha'Yam - they perturb the water via oars used to conduct the ship. The same applies to "Memulach Tahor Kodesh" (Shemos 30:35).
Rashi #3: This literally refers to Shamayim [and Eretz]. See that they are strong and healthy - even so, they will wear out 1 . My virtue and salvation are forever - they are stronger than Shamayim va'Aretz!
Radak citing his father: This is an exaggeration. I would sooner destroy the world than nullify My salvation and Tzedakah. Just like Shamayim and Eretz endure, so My salvation will endure. So Yirmeyah said (31:35) "Im Yamushu ha'Chukim ha'Eleh
Will the land wear out?!
Rashi: Rulers of the land will wear out.
Refer to 51:6:2:3-7.
Who are "Yosheveha"?
Rashi: The other residents of the land (not the rulers).
For whom is "Yeshu'asi"?
Rashi: It is for My nation.
What do we learn from "vi'Yeshu'asi l'Olam Tihyeh"?
R. Yonah (Mishlei 3:26): An aspect of Bitachon is knowing that everything is in Shamayim's hands. He can save from any affliction, instantly. One should hope to him even if a sword is on his neck. He can change nature and switch Mazalos - "Ein la'Shem Matzor Lehoshi'a b'Rav Oh vi'M'at" (Shmuel I, 14:6).
What is the meaning of "v'Tzidkasi Lo Sechas"?
Malbim: The Tzedakah with which I bring the salvation, it does not fear this great destruction (refer to 51:6:2:6), for Tzedakah does not consider the deeds and merits of the recipients. It is pure Chesed