Nahum is one of those little books which you sort of know is in the Bible, but can never find when you want to, and always end up looking in the Contents page. It comes between Micah and Habakkuk – not that this represents when the books were written. It is all about the fall of Nineveh (which you will have heard of from the story of Jonah).
Nahum was apparently originally written as a poem – possible as an acrostic poem (each line beginning with the next letter of the Hebrew alphabet). This has been somewhat lost in our modern translations, though some of the descriptions do read more like poetry than history. It is thought to have been written either just before the downfall of Assyria (making it a prophetic book) or just after (making it a history book) – so dated about 615/612 BC. Most people seem to think it was written after the fall of Thebes (663 BC) and before the fall of Nineveh, and it certainly sounds like a warning to me, rather than a poem about what has already happened.
It seems that although the people of Nineveh had listened to Jonah and changed their ways, about 100 years later, they were back where they started, ignoring God and oppressing people and generally being bad. Nahum says they are going to be destroyed, and sometimes the descriptions are shockingly graphic (not something we ever studied in Sunday School – I would have remembered!)
The basic message, for today as much as then, is that God is holy, and will not tolerate evil forever. He is slow to anger, and he wants people to change and return to him, but he is a just God, and if people continue to ignore him, he will destroy them. God loves justice, and everyone will be judged. Sometimes, when we watch the news, it feels like God has gone to sleep, that awful things are happening and there is no justice. I especially felt this when I saw photographs of the children in Syria being torn apart by the war. However, this book reassures us, that God will act, when the time is right.