Here "your" is singular. Possible interpretations are 1) God is speaking to Isaiah and "your" refers to Isaiah. AT: "your people Israel are" or 2) Isaiah or God is speaking to the nation of Israel and "your" refers to the nation. AT: "your people, O Israel, are" (See: [[rc://en/ta/man/translate/figs-you]])
This emphasizes that there were a great number of people of Israel. AT: "are too many to count, like the sand on the seashore" (See: [[rc://en/ta/man/translate/figs-simile]])
This can be stated in active form. AT: "Yahweh has decreed that he will destroy most of those who live in Israel" (See: [[rc://en/ta/man/translate/figs-activepassive]] and [[rc://en/ta/man/translate/figs-explicit]])
This can be translated as a new sentence. AT: "This must be done for the sake of perfect righteousness" or "Yahweh must do this because he is completely righteous"
Possible meanings are 1) "destroy everything in the land just as he has determined to do" or 2) "destroy the people in the land just as he has determined to do."