Why did He say "Hineni Elayich"?
Radak: Its residents are haughty, and say "who will camp against us?! Who will come in our dwellings?!" I will come to you, and fight with you!
What is "Yosheves ha'Emek"?
Rashi #1: It is Yerushalayim, which is amidst a valley. Radak - it is high, and around it is a valley.
Rashi #2: Hashem made a deep counsel against you, to destroy you.
What is "Tzur ha'Mishor"?
Rashi: It is a mountain, that all around it is plain.
Malbim: [Beis ha'Melech and the fortress were on the incline of the mountain. From the side below it is] fortified and strong like a rock - "who will come in our dwellings?!"
What is the meaning of "Mi Yechas Aleinu"?
Rashi: Who will camp against us?! This is like "Ki Sham Aram Nechitim" (Melachim II, 6:9).
Radak: The root of Yechas is Nachas. If Ches were not a guttural letter, it would have a Dagesh. It means descended and camped. The same applies to "va'Tinchas Alai Yadecha" (Tehilim 38:3). Descending applies to the war, which is in the valley and in the plain, like it says "Oh va'Milchamah Yered v'Nispah" (Shmuel I, 26:10).
Malbim: [Beis ha'Melech and the fortress were on the incline of the mountain. From the side of the mountain,] who will descend from the mountain to come upon us?