Rashi: [Other nations] were not [Yisrael's] brothers, and they did not do evil to them ¹ [yet they drank the cup of punishments]. They do not have a sentence to die like you [Edom] do. (All the more so you will drink it!)

Radak: The punishment is not placed on [other nations] like it is placed on you (Edom), for Yisrael is your brother. All the nations were stricken and punished for doing evil to Yisrael, and Edom, Yisrael's brother, should not have harmed them, rather, helped them according to Edom's ability. Also in Ovadyah (1:10) it says "me'Chamas Achicha Yakov Techasecha Vushah v'Nichras l'Olam." Therefore, Edom should drink the cup of punishments more than other nations.

Malbim: Do not expect Me to sustain [your orphans and widows], for the nations that were not sentenced to drink the cup [of punishments, i.e. their verdict was not to be eradicated), even so, they drank. Once the staff of Hashem's anger went out to provoke kingdoms, it does not distinguish, and destroys everything.

Malbim: You [Edom] are the cause of all this [destruction]. Surely you will not be cleansed!

Malbim: Yes. They will drink and be cleansed. Edom will drink and will not be cleansed!