We're not gonna lie: the speaker of "Arms and the Boy" is a bit of a weirdo. He seems to really want this boy to get a feel for the murderous nature of weaponry, as if he thinks the kid is too much of a softy for modern, manly warfare.
He tells his addressee (who that is is a whole different ballgame) to help the boy understand his weapons' "hunger for blood," and to feel "the sharpness of grief and death" that they have. But why? Why does he want the boy to understand these things?
Well, he seems to think that this kid is a bit of a wimp. He's spent too much time laughing and not enough time killing. He's not fierce enough. So does our speaker really want this kid to become a killing machine? Does the speaker think that's a good thing?
Sometimes, it's hard to tell. Our best guess is that this speaker just wants this youngster to understand just what a mess he's found himself in. War is a place where young men have to grow up really quickly, and this hardened speaker knows that sooner, rather than later, is always better on that front.