Possible meanings are 1) "this" refers to Yahweh sending the people into exile as Isaiah mentioned in the previous verse or 2) "this" refers to the actions that Isaiah will mention in the next part of verse 9.
This can be stated in active form. Alternate translation: "Yahweh will purge the sin from the Israelites" or "Yahweh will forgive the sins of the Israelites" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Here "Jacob" represents the descendants of Jacob. Alternate translation: "iniquity of the Israelites ... removal of their sins" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This speaks of the results of an action as if it were the fruit that grows as on a tree or vine. Alternate translation: "the result" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "he" refers to Jacob who represents his descendants. Alternate translation: "They will completely destroy all the altars on which they sacrifice to false gods, and they will remove all the Asherah idols and the altars on which they burn incense to false gods" (See: [[rc://en/ta/man/translate/figs-metonymy]])