1)
Why did he say "Atah Nora"?
1.
Radak: You will be awesome. All Goyim will fear You from that day and onwards.
2)
Why does it say "u'Mi Ya'amod Lefanecha"?
1.
Radak: It is proper that they fear You, for no one can stand in front of You "when You are angry"!
2.
Malbim: "Hoy Ashur Shevet Api" (Yeshayah 10:5) - from when Hashem sent His anger on the land, no kingdom stood in front of [Melech Ashur]; You were very awesome.
3)
What is "me'Az Apecha"?
1.
Rashi: It is from when You are angry.
