Albert Barnes Commentary Isaiah 34:8

"For Jehovah hath a day of vengeance, a year of recompense for the cause of Zion." — Isaiah 34:8 (ASV)

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.