1)
Verse 20 said that "Amim v'Yoshevei Arim Rabos" will come. Why is this repeated?
1.
Malbim: Here it teaches great nations, not mere individual cities.
2)
How are they Atzumim?
1.
Radak: Their number is awesome. The same applies to "Atzmu Li Almenosav mi'Chol Yamim" (Yirmeyahu 15:8) regarding Bamos. The matter is repeated in different words.
2.
Radak citing Targum Yonasan: They are great [kings].