MALCOLM      Be this the whetstone of your sword. Let grief

Convert to anger: blunt not the heart, enrage it.

MACDUFF      O, I could play the woman with mine eyes,

And braggart with my tongue. But gentle heavens

Cut short all intermission. Front to front

Bring thou this fiend of Scotland and myself.

Within my sword’s length set him. If he’ scape,

Heaven forgive him too.       (4.3.230-237)

Channel your grief into revenge, says Malcolm; be this, your anguish, the whetstone of your sword, to sharpen it. Let grief convert to anger: blunt not the heart, enrage it. This is fuel for your rage; every pang of your anguish a spur to revenge. (Implicitly: that’s also what it means to feel it as a man.) Of course it suits Malcolm to have an enraged, vengeful Macduff on his side, a leader for his cause, not least a rallying point for those equally appalled by the slaughter of his family. He is also, perhaps, being practical, giving Macduff something to do, something to think about, enabling action rather than simply feeling. Macduff, although not in so many words, seems to agree. O, I could play the woman with mine eyes; I could simply sit here and weep, helplessly. Or I could play the braggart with my tongue, extravagantly, wildly swearing vengeance, promising to do terrible things, full of sound and fury, words not deeds. There is so much I could say. But gentle heavens, cut short all intermission. There’s no point in delaying, for any reason, whether it’s to mourn or to articulate my pain and my rage. I’m in. Front to front bring thou this fiend of Scotland and myself. I want to see him, this devil, less than a man, less than human, face to face, I want to confront him, up close, within my sword’s length. I want to look him in the eye, and then kill him. If he escapes me—well, it’ll be a sign that my hatred has somehow abated, that he’s been forgiven even by heaven. And neither of those things is going to happen. From this moment, Macbeth’s a dead man, and I will, I must kill him.