Nahum prophesied against Nineveh over 100 years after Jonah. In the midst of words of destruction and the downfall of the superpower of that time, the prophet cannot but speak of God’s goodness as well.
“The Lord is good –
indeed, he is a fortress in time of distress,
and he protects those who seek refuge in him.
But with an overwhelming flood
he will make a complete end of Nineveh;
he will drive his enemies into darkness.”
Nahum 1.7-8 NET
Note the emphasis in the third phrase, on seeking God. It’s not that God helps those who help themselves. He helps those who seek him.
Verse 8 begins with an adversative conjunction, “but.” God’s goodness does not mean inactivity in the face of evil. On the contrary, his goodness leads him to deal with it for the sake of his seekers.
The “overwhelming flood” could be taken to belong with verse 7 or verse 8, or both, so that the flood becomes both his action of protection and of making an end of Nineveh.
“This might be an example of intentional ambiguity: God will protect his people from the very calamity that he will use to destroy his enemies” (NET Bible).
Perhaps one can go further: God will protect his people by the very calamity that he will use to destroy his enemies. The very action that brings destruction to some means salvation for others. Goodness and severity, then, are not opposite poles of God, but manifestations of his unity, Rm 11.22. In the same breath we can speak of his mercy and his justice, Psa 111.
God is good, and his goodness means severity toward evil. That is our hope.