Art is important in this poem, insofar as the speaker wants us to know that it's not important. Well, it's not important compared to appreciating the time you have on Earth to be in love with a dude in an orange t-shirt. The moments you get to spend with your One True Love, for our speaker, are life's greatest treasures, and no Renaissance drawing or French painting can even come close. There are a variety of examples of art that O'Hara, himself an art critic and museum curator, offers up in this poem. All of them fall short, though, in in that way they collectively come to stand for what the speaker sees as a fundamentally distracted, wrong-headed approach to life. Life is about loving someone, not representing them with art.
Line 6: The speaker and his beloved "take on" secret smiles in front of statuary. It's as though they share a kind of private insight when they're confronted with this sort of art. What might that insight be? In essence, love > art.
Line 8: Not only does statuary give them the chance to share an inside joke, it's downright "solemn" and "unpleasantly definitive." When compared to the living, breathing object of your love, a statue is just excruciatingly boring.
Line 11: It's not just statuary that disappoints the speaker. Portraits lose all meaning for him, too. Next to his beloved, they're "just paint."
Line 14: What's more, the speaker gets more joy and pleasure out of looking at his beloved than by looking at any portrait in the world. So there, portraits—take that!
Line 15: Well, let's not get carried away. This is a funny line, one that undercuts the almost too-sugary line before it. All the same, the speaker suggests that "The Polish Rider" might "possibly" be more fun to look at, and then only occasionally.
Lines 17: In other equations, the beloved's movements > Futurism. A whole school of art dedicated to celebrating motion, energy, and excitement really just can't hold a candle to the movements of our speaker's beloved. Ain't nothing like the real thing, baby.
Lines 18-19: More specifically, the beloved's movements trump some of the most famous art studies of the human form, from Leonardo and Michelangelo's drawings to Duchamp's "Nude Descending a Staircase."
Lines 20-23: Even the Impressionists—and everyone, even folks who don't like art, loves the Impressionists—got it wrong. Just like sculptor Marino Marini, they did not have the right models to pose for them. Who would the right models be, we wonder? It's likely our speaker would say that an artist's only model should be the person you love. The trick is, he'd say, if you fall in love with someone, don't waste your time making art about it. Enjoy your time together. Go out and have a coke, or something.