1:3-5
The Lord is slow to anger. In fact the first part of this verse is almost word for word from Ex 34:6,7. There the words are addressed to Israel, here they are addressed to Israel (or Judah, to be more precise), but are explaining His treatment of Assyria. Many years before God had sent Jonah to Nineveh, and they had repented for a time. Peter tells us that God does not show favouritism, and here we have an example of that. He was patient with Assyria. But He is not patient forever, there comes a point when judgement must come. Nor is His patience a sign of weakness, but a sign of strength. We may often wonder why God is being so slow to deal with an issue, or with a person! He may well be giving them time to repent. On the last day no one will be able to claim that God acted too rashly.
Natural events are not just random events, they are all subject to God’s control, and are sometimes used as instruments of His judgement or of His salvation. All of creation is subject to the Lord.
1:6
“Who can withstand His indignation?” Judah needed to know that Assyria would not be able to withstand the Lord’s anger, nothing can protect against His wrath. In Isaiah 36-39 we read of the events when Assyria was right at the walls of Jerusalem, and this ended in Assyria being defeated. So Judah should fear the Lord, not Assyria, and these words of the Lord are a double edged sword. For Judah’s primary need was to repent of her own sins. Like Assyria, there were some brief times of repentance, and in these times Judah received mercy, but she always reverted to type, sinning all the more against the Lord. So she too would one day be subject to His irresistible wrath, as happened with the Babylon conquest.