Geoffrey Chaucer, the medieval poet, defined wrath like this: “Wrath is a wicked will to be avenged in word or deed.” Anger and wrath are not the same animal. Anger can be a holy response to evil; God himself is slow to anger but capable of it. Wrath is something narrower and uglier. Wrath is anger that has gone shopping for revenge. It is the heart that has moved past being grieved by sin and has begun planning how to make someone pay.
Frederick Buechner described what it feels like to live in that state. He called anger “possibly the most fun” of the seven deadly sins, savoring grievances long past and bitter confrontations still to come. The trouble, he said, is that what you are wolfing down at this feast is yourself. The skeleton at the table is you. Doriani points out that this is precisely what Jesus is exposing in verse 39. The slap on the right cheek in the first century, France and Keener both note, was a backhanded blow, an insult to honor rather than a serious physical attack. Jesus is putting his finger on the moment your honor takes a hit and your hand starts to ball into a fist.
The first move toward freedom is to name what is in you. Not just irritation, not just frustration, but the wicked will to be avenged. Before you can stop the cycle in the world, you have to stop it in your own chest. And that requires a category for sin you may not have used in a long time.