Why does it say that Azah will be Azuvah?
Rashi: If you will do so, I will command about your evil neighbors Peleshes, Amon and Mo'av, like it says here.
Radak: The words Azah and Azuvah are similar, even though not all the letters are the same; this is an eloquent expression.
Malbim: This teaches that Yom Hashem will include all nations - "Hichrati Goyim Nashamu Pinosam...; Amarti Ach Tir'i Osi Tikchi Musar" (3:6-7).
What is the significance of "ba'Tzaharayim Yegarshuha"?
Rashi #1: Ashdod is its name; "mi'Ketev Yashud Tzaharayim" (Tehilim 91:6) will expel them, to be Shedudah (plundered).
Rashi #2: It was a pasture for flocks. Tzaharayim is harsh for flocks to go out (due to the heat) - "Eichah Tarbitz ba'Tzaharayim" (Shir ha'Shirim 1:7).
Radak: Enemies will expel the congregation of Ashdod suddenly, just like ha'Ketev Yashud ba'Tzaharayim. Since Yashud is associated with Tzaharayim (Tehilim 91:6), it is as if the expressions are similar.
What is the significance of "Ekron Te'aker"?
Radak: The words are similar.
Four of the five Sarnei Pelishtim (Yehoshua 13:3) are mentioned. Why is Gas omitted?
Radak: It was in the hands of Malchei Yehudah.
Malbim (Amos 1:8): It belonged to Yehudah.
