All the new thinking is about loss. In this it resembles all the old thinking. (lines 1-2)
The "new thinkers" are a hip, fashionable crowd; they want to be on the cutting edge of philosophy. But, they don’t realize that "loss" is a topic that philosophers covered for, oh, about 2,000 years. That’s the way fashion works. What was old goes out of style, and then comes back into style again once people forget about it. The "old thinking" here goes all the way back to Plato, the most influential philosopher of ancient Greece and, probably, of all time.
The idea, for example, that each particular erases the luminous clarity of the general idea. That the clown- faced woodpecker probing the dead sculpted trunk of that birch is, by his presence, some tragic falling off from a first world of undivided light. (lines 3-8)
Plato really liked to use metaphors of light and darkness. Check out his "Allegory of the Cave," and you’ll see what we mean. Knowledge is light, enlightenment, illumination. Ignorance is all darkness and shadows. The speaker ironically talks like a Platonist in this quote by describing the "general idea" as a "luminous clarity." This sounds pretentious, and it’s supposed to. The "particular," that is, particular things, is like a big oaf that gets in the way out of the light, and you want to say, "Hey, you! Get out of the way! I’m trying to think about ideas here!"
The world of ideas is considered to be original and perfect by the Platonists. It is a "first world" where light is "undivided," unlike earth, which is part-light and part-darkness. In this view, the poor woodpecker, because it exists on earth, is just a shadowy example of some perfect idea of a Woodpecker. But, we’re pretty sure it doesn’t care one way or the other.
After a while I understood that, talking this way, everything dissolves: justice, pine, hair, woman, you and I. (lines 14-16)
Talking like a Platonist means that words always refer to perfect ideas which don’t exist in our world. But, if these things don’t exist in the here-and-now, what’s the point of talking about them? If you’re really a die-hard Plato groupie, even everyday meanings "dissolve," like a sugar cube in a glass of water.
There are moments when the body is as numinous as words, days that are the good flesh continuing. (lines 28-29)
Plato prefers the spiritual world of ideas, which is "numinous" or "heavenly," to the world of pesky "particulars," like bodies. But, the speaker claims that the body can be numinous, too – at least, sometimes. The two worlds aren’t strictly separate.