God’s slowness to anger must not be confused with any weakness or ambivalence. 
Today’s reading: Nahum 1-3; Revelation 13
2 The Lord is a jealous and avenging God;
the Lord is avenging and wrathful;
the Lord takes vengeance on his adversaries
and keeps wrath for his enemies.
3 The Lord is slow to anger and great in power,
and the Lord will by no means clear the guilty.
His way is in whirlwind and storm,
and the clouds are the dust of his feet. Nahum 1:2,3
7 Also it was allowed to make war on the saints and to conquer them. And authority was given it over every tribe and people and language and nation, 8 and all who dwell on earth will worship it, everyone whose name has not been written before the foundation of the world in the book of life of the Lamb who was slain. Revelation 13:7-8
If there is anything we can learn from reading the Bible carefully from cover to cover, it is that God is firmly in control of all of human history. Nothing escapes His knowledge, His presence, or His power. He is omniscient, omnipresent, and omnipotent. That does not mean that He accepts everything that happens with no further action. He will act in His time to reward faithfulness and punish all evil.
In Nahum’s day, the nation of Assyria was imposing her power on the surrounding nations. Israel had already fallen to her, and Judah, under King Manasseh, was a vassal state. Nahum proclaimed the power of God in the midst of this difficult situation. Assyria would fall, he assured them. God is slow to anger but not weak in power. He would pour out His wrath. Meanwhile, Nahum, whose name means comfort, reminded Judah that “ The Lord is good, a stronghold in the day of trouble; he knows those who take refuge in him” (1:7).
In John’s vision, he sees two beasts, one from the sea and one from the earth. These are united with the dragon and they wreak havoc on God’s people, who do not take the mark of the beast which gives access to commerce. It seems like a hopeless situation, yet there is a limit on the time allotted to these beasts. There is a reassurance to those who refuse to worship the beast. Their names were recorded before the foundation of the world in the book of life of the Lamb who was slain. Let this bring comfort to us who believe but warning to all who confuse God’s patience with any kind of weakness.
 The Reformation Study Bible, introductory notes to Nahum, p. 1587