What is the significance of an iron pan?
Radak: It is flatter than a pot and other iron Kelim, to compare it to a wall.
Malbim: This shows that there was an iron wall between the Navi - Hashem's messenger, and the city. Their sins divided like an iron wall between Hashem and the messengers of His Hashgachah, and the city.
What is the significance of an iron wall?
Rashi: It is a semblance of the city wall that separates between the army and the city.
Radak: (a) The heart of Yisrael is strong like iron. (b) It is black, to hint to Yisrael's sins, which are black and ugly; they are compared to black figs. They are far from whitening. They divide between Yisrael and Elokim like a wall separates between houses.
Why did He say "va'Hachinosah Es Panecha Eleha"?
Radak #1: Hashem's face is towards them, if they will return to Him.
Radak #2: This is like "v'Samti Ani Es Panai ba'Ish ha'Hu" (Vayikra 20:5).
Malbim: This hints that via this wall, Hashem prepared His face towards it via His Nevi'im that He sent to it each day.
Why does it say "v'Tzarta Aleha"?
Radak: He said that it will be besieged, until its walls fall.
Malbim: (It already said "v'Haysah va'Matzor.") The repetition hints to a double siege. (a) A siege of the Nefesh, via the Nevi'im who besiege it each day to return them to the good path. (b) The siege of the enemies. Via the iron wall, the enemies besieged it, for Hashgachah departed from it. Since He put His face to the city, therefore you should besiege it, to return them to the good. If the Navi will conquer the city, the enemies will not conquer it. If he will not conquer it, rather, the iron wall will remain between him and them, then the enemies will conquer it.
What is the Os to Bnei Yisrael?
Rashi: Yerushalayim will be besieged.
Radak: The enemies will besiege Yerushalayim until they cleave it.
Malbim: Refer to 4:3:4:2.