Nahum seems to be quoting from Exodus 34:6–7 where the Lord says to Moses, The Lord, the Lord, a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness, keeping steadfast love for thousands, forgiving iniquity and transgression and sin, but who will by no means clear the guilty, visiting the iniquity of the fathers on the children and the children’s children, to the third and the fourth generation.
However, there is no mention of forgiveness in Nahum’s use of these verses. Assyria has passed the point of no return.1 Indeed, the Lord is slow to anger, but his mercy and slowness must not be mistaken for weakness in the face of his enemy. He is both great in power and will by no means clear the guilty.
3 L'Eternel est lent à la colère, il est grand par sa force; Il ne laisse pas impuni. L'Eternel marche dans la tempête, dans le tourbillon; Les nuées sont la poussière de ses pieds.