Here "your" is singular. Possible interpretations are 1) God is speaking to Isaiah and "your" refers to Isaiah. Alternate translation: "your people Israel are" or 2) Isaiah or God is speaking to the nation of Israel and "your" refers to the nation. Alternate translation: "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. Alternate translation: "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. Alternate translation: "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. Alternate translation: "This must be done for the sake of perfect righteousness" or "Yahweh must do this because he is completely righteous"