Why does it say "Ki Hu Elokim Elokeinu"?
Radak: Because He is Elokeinu, we will have this great Tovah.
Malbim: He is Cheil v'Chomah" (Eichah 2:8; the small wall and the big wall), He is the Guard on top of the castle to guard it - "Elokim b'Armenoseha Noda l'Misgav" (verse 4)!
What is "Al Mus"?
Rashi: It is like one who leads his small son slowly.
Rashi citing Menachem (from Yerushalmi Mo'ed Katan 3:7): It is an expression of Olam; He will conduct us forever.
Radak #1: Until death [He will conduct us with this honor].
Radak #2: We can explain it like one word, like Elem and Almah (youths). It is as if k'Almus; the prefix Kaf of comparison is omitted, like "Lev Some'ach Yeitiv Gehah" (Mishlei 17:22; it means k'Gehah, like a cure). He will conduct us like in the days of our youth. I.e. just like He led us before, when He chose us and took us for His portion. We find one word written as two words, e.g. "Yefe Fiyah" (Yirmeyah 46:20).
