Stanza 3 Summary

Get out the microscope, because we’re going through this poem line-by-line.

I look

Okay, take a deep breath. There's a lot to tackle here. Let's see… we have the "I" of the speaker. And the speaker… looks. Yup, pretty much sums it up.
But does it, really? Why do these two words get their very own line all to themselves? What's so important about the speaker looking?
Well, what's he been looking at so far in the poem? He's looked at statues, at portraits, at the "warm New York light," and at you" Come to think of it, the speaker's done a whole lot of looking in this poem. It's seems to be the primary way he accesses the world around him. And what's his favorite thing to look at? Well, it's you, of course. It is a swoony love poem after all.

at you and I would rather look at you than all the portraits in the world

We knew it. This enjambment carries over from the last line and lets us know that you are, indeed, the speaker's favorite thing to look at—at least compared to portraits, anyway. We mean, there's no other portrait in the world that our speaker would rather clamp eyes on… is there?

except possibly for the Polish Rider occasionally and anyway it's in the Frick

Well, okay. Maybe there is one portrait that he'd rather look at, than you. But he'd only "possibly" prefer it to you "occasionally." So, don't get all bummed out.
The portrait in question is "The Polish Rider," painted by Rembrandt some time in the 1650s.
The speaker lets us know that this portrait hangs in the Frick Collection, which is also in New York City.
He tells us this as kind of an aside, by saying "anyway." That word "anyway," is something you might say to someone in conversation, as in "Anyway, that's why I can't eat creamed spinach on the weekends anymore." It's a verbal kind of tic, not something that you would expect to read in a proper poem, right? (For more on O'Hara's conversational tone, go check out the "Sound Check," "Form and Meter," and "Calling Card" sections. Then come back here.)

which thank heavens you haven't gone to yet so we can go together the first time

We've got another enjambment here, which carries over from the last line to give us more gushy lovestuff.
The speaker's just plain pumped that his main squeeze, the object of his affections, the light of his life has never ever ever… been to the Frick.
Okay so why is that so exciting? Simple. Because it gives him the chance to enjoy another special, memorable moment with "you."

and the fact that you move so beautifully more or less takes care of Futurism

Know what else? You are a beautiful mover. Has anyone ever told you that? Well, now the speaker just has. The addressee moves so beautifully, in fact, that the speaker can pretty much stop paying attention to Futurism. Sweet!
What's Futurism? We thought we'd never ask. Futurism was a school of art that emphasized motion, excitement, speed, and energy. It was all about capturing movement (which can be tricky in a two-dimensional, frozen picture).
Still, the addressee moves so wonderfully well that nothing produced by a futurist artist can compare.

just as at home I never think of the Nude Descending a Staircase or

We confess. We used to think that the nude descending a staircase meant our exhibitionist upstairs neighbor, but no! It turns out that this is a very famous painting by French artist Marcel Duchamp. Though not a Futurist himself, Duchamp's technique in this painting was all about capturing the motion of someone going down a set of stairs, but in one single, painted frame.
It's pretty spectacular, we think. But the speaker pays it no mind when he's at home. We're guessing he's got other things on his mind, like, you know, you.

at a rehearsal a single drawing of Leonardo or Michelangelo that used to wow me

Enjambment strikes again. Guess what else the speaker never thinks of? Those amazing and amazingly famous drawings by Renaissance masters Michelangelo and Leonardo da Vinci.
Yeah, there was a time when they floated his boat. But now, not even one of them matters to him. No more boat-floating for those guys.

and what good does all the research of the Impressionists do them

The Impressionists are those painters whose work you are most likely to see on a college poster. You know, those sorta fuzzy, soft-figured scenes that make you sigh a little inside? That's probably them.
Claude Monet is among the most famous Impressionists, and he, like the others, was really interested in how different qualities of light (morning light, dusk light, bright sunlight, cloudy light, nightlights, highlights… oh, sorry, we got carried away there) could be captured in art.
Some Impressionists spent their whole careers in the pursuit of this study, but here our speaker just pooh-poohs it. Pooh-pooh, he says. What good did all that studying produce? (We have a feeling that we're in for another enjambment… )

when they never got the right person to stand near the tree when the sun sank

We are in for another enjambment. This line carries over from the previous one to tell us the reason why those Impressionists were just wasting their time: they didn't have the right model.
Sure, you had the sunset and you had the tree, but without the right person to pose for you, the speaker says, it ain't worth a hill o' beans. (Side note: Beans do not make good hills. They keep spilling all over the place.)
This criticism is a familiar one. Once again, our speaker is slagging off a group of artists, and once again, he's got the same complaint—that they're just missing the point. For our speaker, art just ain't the same if the right person is not involved in it.

or for that matter Marino Marini when he didn't pick the rider as carefully

With this line, the reader tells us that the same goes for poor Marino Marini, who was a sculptor who created several versions of people riding horses. "Oh, Marino, Marino," the speaker seems to say, "nice try buddy, but in the end, it's just not cutting the mustard." Again, the problem is that he didn't pay close enough attention to the person in the art work. What did he focus on instead? Let's read on…

as the horse

"Less horse, more rider!" says our speaker. Why does he use a whole, separate, enjambed line to tell us this, we wonder. Maybe it's because the poem literally separates "rider" from "horse" by putting them on different lines. Even though both are part of Marini's sculptures, clearly (to our speaker) the artist is paying too much attention to one, and not enough to the other.
Whatever the case, our speaker thinks that this art is mere… wait for it… horseplay. (We're sorry. We really are.)