Why does it say "Ki"?
Radak: This is why their counsel about Yerushalayim will not last. Hashem will strengthen those who believe in Him and sanctify His name.
Malbim: Hashem said this to me at the time that Nevu'ah overpowered me.
What is "b'Chezkas Yad"?
Rashi: Nevu'ah overpowered me, when He spoke to me further about this - "va'Yosef Hashem Daber Elai" (5). We find "v'Yad Hashem Alai Chazakah" (Yechezkel 3:14) it is an expression of Nevu'ah.
Radak: It is a strong Nevu'ah, i.e. an awesome and wondrous prophetic vision.
What is the meaning of "v'Yisereni mi'Leches
Rashi: He warned me not to be in the counsel of Shevna ha'Sofer and his supporters. They conspired to rebel against Chizkiyah (Sanhedrin 26a). There is a hint to this below (22:15) "Lech Bo El ha'Sochen."
Radak #1: He warned me not to go in the way of this nation who despise Malchus Beis David due to fear of these kings.
Radak #2: He warned me to go only in the way of Hashem, and to tell and warn others not to go in the ways of the nation that rebels.
