For it is the day of the Lord’s vengeance - A time when Yahweh will take vengeance.
The year of recompenses for the controversy of Zion - The time when he will recompense, that is, punish those who have had a controversy with Zion.
Related Commentaries of Isaiah 34:8
Isaiah 34:8
8 For it is the day of the LORD'S vengeance, and the year of recompences for the controversy of Zion.