Why does it say "Chashav Hashem Lehashchis"?
Rashi: It crossed His mind to do so a long time ago - "Ki Al Api v'Al Chamasi Haysah Li ha'Ir ha'Zos
What is the significance of stretching a line?
Rav Sadya Gaon: Just like Hashem decreed to destroy the wall of Kahal Tziyon, so He stretched a measuring line to destroy [Kahal Tziyon], and did not retract.
Rashi: It was a line of judgment to exact payment for our sin.
Rid: It is a line of desolation. Ri Kara #1 - this is like "v'Nata Aleha Kav Tohu v'Avnei Vohu" (Yeshayah 34:11), "v'Natisi Al Yerushalayim Es Kav Shomron" (Melachim II, 21:13) - the decree of [the exile of] Shomron.
Ri Kara #2: He stretched against them Midas ha'Din.
Palgei Mayim: Hashem thought to destroy it from when the builder's line was stretched - "Ki Al Api v'Al Chamasi Haysah Li ha'Ir ha'Zos l'Min ha'Yom Asher Banu Osah" (Yirmeyah 32:31).
What is "Bale'a"?
Rav Sadya Gaon, Rashi: It is destroying.
What are "Chel v'Chomah"?
Rashi: They are a small wall and a big wall.
Ibn Ezra: Chel is a place around the wall, like "va'Ta'amod b'Chel" (Shmuel II, 20:15).
How did He make Chel v'Chomah mourn together?
Rav Sadya Gaon: He made the people of the Chel v'Chomah mourn, when they were destroyed together.
What is the meaning of "Umlalah"?
Rid: It is an expression of cutting off - "Umlal Ani" (Tehilim 6:3).
Ri Kara: It ceased. Likewise, "u'Ferach Levanon Umlal" (Nachum 1:4) - it ceased to make fruits like it used to. "V'Rabas Banim Umlalah" (Shmuel I, 2:5) - she ceased to give birth.