Why does it say "v'Atah"?
Rashi: After all this, Hashem said not to fear.
Radak #1: Some say that this refers to Koresh Melech Paras. He sent Yisrael from Galus Bavel.
Radak citing his father: This refers to Sancheriv 1 . It is connected to the Parashah above - a fire will burn around (42:25). Now it promises Yerushalayim's residents [protection] from Sancheriv.
Radak #2: We can say that this Parashah refers to the future 2 .
Malbim: In spite of all this, do not despair.
Why does it say "Bora'acha Yakov"?
Radak: Recognize that I created you, and the world.
Malbim: Beriyah is creating substance from which matters are formed. Yisrael are called Yakov when they are at a low level. They are called Yisrael when they are esteemed, and are conducted miraculously. Initially, the beginning of the nation (their substance) is Yakov; their essential form is Yisrael - they rule over nature. Refer to 43:1:3:3.
From what did Hashem redeem you?
Radak #1: From Sancheriv's sword. He will not capture Yerushalayim.
Radak #2: If this refers to the future, I redeemed you from Galus.
Malbim: From Egypt. I chose you for [My] nation; this obligates Me to redeem them again, for they are My servants, and not Nebuchadnetzar's.
Why does it say "Li Atah"?
Radak: It is upon Me to redeem you.
Malbim: Based on "Yotzercha" (your form) I called you Yisrael, and you are to Me; you are under My Hashgachah, and not under nature and the Heavenly legions.