Why will He roar from Tziyon?
Rashi: He will roar due to what they did to Tziyon.
Radak: His Shechinah is there, in Yerushalayim. It is as if He roars from there and puts His voice on them.
Malbim: Conduct and Mishpat come from Tziyon. Sha'agah is a great voice, the opposite of a low voice. The primary Shechinah is in Tziyon - there He will roar in a great voice.
Why does it add "umi'Yrushalayim Yiten Kolo"?
Malbim: Nesinas Kol need not be a great voice, just it is not silent. Yerushalayim is not as Kadosh as Tziyon; there, He will not roar in a great voice, but He will not be silent. 'Giving His voice' is Divine conduct.
What is the significance of "Ra'ashu Shamayim va'Aretz"?
Rashi (from Mechilta Beshalach 2): He will exact payment from the Sarim of the nations above, and afterwards from the nations.
Radak: This is the consequence of putting His voice on them. It is a Mashal. On that day will be also noise in Eretz Yisrael, like it says in the Nevu'os of Yechezkel (38:19) and Zecharyah (14:5).
Malbim: This will result from His roaring. Conduct of nature in the land, and conduct of the Ma'arachah of Shamayim, will cease.
What is "Machseh"?
Rashi: It is an expression of covering; it is a shelter. Radak - He will shelter them from the nations, and from the noise, lest they harm Yisrael.
Malbim: He is a shelter for His nation, to save them from all evil.
Why does it add "u'Ma'oz li'Vnei Yisrael"?
Malbim: The name Yisrael shows that they are above nature - "Ki Sarisa Im Elohim" (Bereishis 32:29). He will be strength for them - they will overpower with His strength. This is more than a shelter!
