Why does it say that Yisrael will be Shelishiyah to Egypt and Ashur?
Rashi: It will be a third nation for Shalom and Brachah. At that time, there was no nation in the world as esteemed as Egypt and Ashur, and Yisrael were lowly in the days of Achaz and Hoshe'a ben Elah. The Navi says, via the miracle that will be done for Chizkiyah, Yisrael's name will rise, and they will be esteemed like one of these kingdoms for Brachah and grandeur.
Radak: It will be the third member of the trio (with Egypt and Ashur) of nations with Emunah in Kel.
Malbim: Yisrael will be blessed triply, via Egypt and Ashur 1 , in three matters.
Why does it say "Brachah b'Kerev ha'Aretz"?
Radak: They will be blessed more than other nations, as long as they persist in Emunah in Kel.
