To no real purpose (of course, a poem should not mean but be), I've been reading and re-reading this Elegy. It's "for Fortinbras" but it's actually Fortinbras elegizing Hamlet. I'm altogether fascinated by the enjambment, the poetical technique of flowing the syntax of lines together to create a dual meaning, something we don't do much in prose (but Your Fearless Blogger determined to make it so). Anyway, I take this back to the notion of "form as metaphor." The emjambment, that flowing together, amplifies what Shakespeare did in the play between these two, where Fortinbras the bold soldier-prince is a foil for Hamlet the thoughtful philosopher-prince.
That is, the formal technique of enjambment is a metaphor for the complex relationship between these two. See that Herbert goes between stressing the differences between the two (separate "sentences" in enjambment) to stressing the similarities (the flowing together in lines). The relationship between the two isn't even clear, but it's a relationship-- are they lovers (I could never think of your hands without smiling) or just fellow princes (Now that we’re alone we can talk prince man to man) or opposites (You will have a soldier’s funeral without having been a soldier/the only ritual I am acquainted with a little, or each other's futures (both will be "black ants). Enjambment is a physical, concrete way to show that intangible connection.
Form doesn't just follow function, as the architects say. Form reinforces the message. It's a metaphor for the message. This is, if possible, even more important in popular fiction, which relies on the traditional storytelling forms to reflect something deep and essential and universal about the human condition or human nature. The form of a genre or tradition is a manifestation of the underlying theme or message. So the battle between the doctor and the monster in Frankenstein, for example, is a common metaphor in horror for the battle between the "good self" and the "bad self" within each of us.
What is the "surface" metaphor in your storytelling tradition, and what does it reflect? I really believe thinking this through might help us deepen the subtext of our stories.