VENGEANCE OF GOD

"Vengeance in the Old Testament is a juridical term involving the righting of wrongs that have been done. Earlier, Nineveh experienced God’s grace because they had repented. Now they will experience his vengeance. The outpouring of God’s wrath has been delayed, not because he does not care or because he was helpless to act, but because he is patient and slow to anger. The fact that Nineveh is not specifically mentioned in chapter 1, yet seems clearly to be in view, indicates that she serves as an example of the way God deals with his enemies in general. He will not leave the guilty unpunished. This is quoted from Exodus 34: 7 and forms the necessary counterpoint to God’s grace as described in Exodus 34: 6. The nation or individual who rejects God’s forgiving grace will of necessity experience the outpouring of his wrath. God will have the last word. A Jonah may be impatient with God for sparing a Nineveh for a time, but God’s people may rest confidently in his determination and power to deal with sinners in his own time and way. The awesome and irresistible power of God is displayed in nature (1: 3b–6). If the most powerful forces of nature are at God’s disposal to be used as his instrument of judgment, and if no area of creation is immune to the fierceness of God’s wrath, how will any person or kingdom be able to withstand God’s judgment?"
~~ Commentary on Nahum, Baker's Illustrated Commentary of the Bible .