Why did he leave from Sha'ar ha'Gai?
Malbim: Nechemyah's house was there. This is clear from below (12:31, 38), that the two Korbanos Todah, one of them went to the right of Sha'ar ha'Ashpos, and the other to the left of Migdal ha'Tanurim. Both of them left from Sha'ar ha'Gai, which was between them (3:11, 14), for the Pechah's house was there. Sha'ar ha'Gai was in the west. He left his house to the south and passed Ein ha'Tanim to Sha'ar ha'Ashpos, which is 1000 Amos (3:11).
What is the meaning of "va'Ehi Sover"?
Rashi: I was Shover 1 (broke, to breach it more).
Ibn Ezra: This is like "va'Yisbar Lehashnaya", like Sevara. I contemplated and investigated the walls.
Malbim: I wanted to test if the old walls are strong, and there is no need to break them and rebuild them, only to fill the breached places ? "Ki Hechelu ha'Perutzim Lehisasem" (4:1). This implies that where it was not breached, they left the old wall. He pressed with his hand, to see if it would break the wall.
Minchas Shai: In Rashi's text, it says Shover. The text of Ibn Ezra and Redak is Sover. The Mesorah supports them; it says that we find this only twice.
What do we learn from "Asher Hem Perutzim"?
Rashi: Where it was breached, they breached it more.
Ibn Ezra: Ha'Mefuratzim is one word. This is like "Mazeh b'Yadecha", "Mahlachem Tedake'u Ami 1 ."
Ibn Ezra citing Ba'alei ha'Mesores: We divide it into two words to shorten them, and expound that the open (non-final) Mem hints that the walls were open and breached 2 .
Why does it mention that the wall was burned?
Rashi: Therefore, it was easy to breach it more.
