The nations will be saved. They will come to the light (Isaiah 60:3). How? We can work backward through Isaiah.
They come into the light that shines from Israel. That light is the light of Yahweh Himself dwelling among and shining through His translucent people.
Israel becomes that light after Yahweh takes up His armor against wickedness in Zion. A city of righteousness becomes the city of light (ch. 59).
And that means that Zion becomes a city where yokes are broken, where bread is shared, where the naked are clothed and the homeless housed (ch. 58). Yahweh’s light is refracted through Israel as generosity, justice, mercy, kindness.
Zion can only become that city because Yahweh delivers her from her own transgressions. Once He delivers her, she becomes a light on a hill, drawing the nations.
Here, Isaiah’s “atonement theory” is about Yahweh’s victory, His restoration of Israel, and, through Israel, the nations.