In God’s revelation of himself to Moses on Mount Sinai, he says that he is “slow to anger” (Exodus 34:6). However, later in the Old Testament, in the prophecy about Christ in Psalm 2, we are told to “Kiss the Son, lest he be angry, and you perish in the way, for his wrath is quickly kindled” (2:12).
So which is it? Is God slow to anger or is he quick to wrath? It can’t be both, can it?
It seems to me that the answer lies in understanding that there is a distinction between “getting angry” and “kindling wrath.” Getting angry refers to the attitude God has toward his creation. Kindling wrath refers to the ways in which he acts out that attitude.
In this sense, we can affirm both: God is slow to become angry, as he tells Moses on Mount Sinai (and repeats throughout the rest of Scripture (see Nehemiah 9:17; Psalm 86:15, etc.). But after he is angered, his wrath, the means through which that anger is manifested, can be kindled quickly.
Romans 2:4-5 captures this distinction powerfully. After mentioning how the people have been presuming upon “the riches of [God’s] kindness and forbearance and patience” (referring to the slowness of God’s anger), Paul says that they are storing up wrath for themselves “on the day of wrath,” which, as we know from Paul’s words in 1 Thessalonians 5:2, will come quickly, “like a thief in the night.”
Ultimately, each of these is true and each of them is a blessing to us. The fact that God is slow to anger means that there is time and opportunity for us to repent of our sin. The fact that he is quick to wrath guards us against presuming upon his mercy and prolonging our rebellion.