Moore's "What Are Years": How Does This Poem Be?

In the midst of the energetic discussion around the recent "Listening to Poetry" post, I happened to come across the following extraordinary poem again. It was in a wonderful format, an illustrated anthology called Parallels: Artists/Poets published by MidMarch Arts Press, accompanied on the facing page by an abstract charcoal sketch by Claire Heimarck. I found myself staring face to face with the poem, and I couldn't stop re-reading it —in part because, as far as I can tell, it belied everything I had been saying.

W.H.Auden and Marianne Moore

My post was about listening to poetry, reading it with the musical part of the brain, as I might do with a poem by Auden. But really, it was about ways that poetry takes us into "the zone"—that place of oneness of being that is so hard to describe but that we recognize when we are there. Moore's poem was taking me into the zone, but not in any of the ways I had been describing.
Certainly the rhetorical stringencies and the idiosyncratic idiom, playing off of the syllabic constraints, are part of what's going on—but how much does that really tell us? What makes Moore's poem vibrate and hum in its own beingness, feeling while behaving and continuing while surrendering, steeling its form straight up, just in the way it itself describes?
If logic can be used to create a sense of the zone (as some of Kay Ryan's do, though in a less strange and stringent way than Moore), then "What Are Years" may be working in a way like that. Something like a Zen koan, it twists the logical brain into knots and then takes a deep breath and lets us stand back with it to take a detached look at its handiwork. Or maybe not.
John Ciardi asked, "how does a poem mean?" while Archibald MacLeish said "a poem should not mean, but be." But I have a different question about "What Are Years": "how does this poem be?"
What Are Years
What is our innocence,
what is our guilt? All are
naked, none is safe. And whence
is courage: the unanswered question,
the resolute doubt, —
dumbly calling, deafly listening—that
in misfortune, even death,
encourage others
and in its defeat, stirs
the soul to be strong? He
sees deep and is glad, who
accedes to mortality
and in his imprisonment rises
upon himself as
the sea in a chasm, struggling to be
free and unable to be,
in its surrendering
finds its continuing.
So he who strongly feels,
behaves. The very bird,
grown taller as he sings, steels
his form straight up. Though he is captive,
his mighty singing
says, satisfaction is a lowly
thing, how pure a thing is joy.
This is mortality,
this is eternity.