Why does it say "Shamati Cherpas Mo'av..."?
Malbim: Also Amon and Mo'av will be punished due to Yisrael.
How did they revile My nation?
Rashi: When they were taking Yisrael to Galus, to Eretz Kasdim, they passed by Amon and Mo'av, and they saw Yisrael crying, moaning and screaming. They taunted them - why do you cry? You return to the other side of the river - your ancestors loved there!
Malbim: Mo'av reviled Yisrael, and Amon blasphemed their Torah and Kedushah.
What is the meaning of "va'Yagdilu Al Gevulam"?
Radak #1: They raised their mouths in jest when Yisrael passed by their borders.
Radak #2: They spoke deridingly about Yisrael's borders - they saw Eretz Yisrael desolate.
Malbim: Amon took from Yisrael's borders, like it says in Amos 1:13 and Yirmeyahu Perek 49. Via this, they blasphemed also Kedushas ha'Aretz and Yisrael's creed, like we explained in Yechezkel Perek 25.