You could think of this poem as a sort of argument about being naked. Who would argue with nakedness? We know; it's a fair question. But Robert Graves is thinking through how to distinguish between different ways that the body gets described in our world. Believe us—that's a lot to pack into four little stanzas.
Here's the problem, as our speaker sees it: there are good kinds of nudity and "bad" kinds. The "good" kinds get depicted in paintings and talked about in terms of form, aesthetic value, or beauty. The "bad" kinds get judged as disgusting or tawdry or just slutty. What's the difference between the two? Well, as Graves reminds us, beauty—or nudity—is all in the eye of the beholder.
In fact, to prove his point, he trots out a whole cast of characters who all have a relationship to the naked body: a lover, a doctor, and even a goddess. And then, to counter these pretty awesome folks, he introduces the tantalizing (and oh-so-seductive) nude form—the kind that gets discussed in the art world. You never hear of a "naked," do you? No. You hear about a nude. And that's why there are so many cultural trappings added on the nude that make it desirable and, well, just better than being naked.
Or is it? Is nudity really all that different? Well, lexicographers (the folks who write dictionaries) don't think so. And by the end of the poem, Graves doesn't think so either. But it's not that the words mean the same thing. "Nude" still seems more cultured, more artistic a term than "naked." It's not just a different word. It's a different set of associations about the body. But whether you're nude or you're naked, you're going to die someday. And even nudes might get what's coming to them in the afterlife.
Sound like a harsh pronouncement? Well, it kinda is. But it's disguised in so much witty banter that it almost sounds like a joke. And we're betting that Graves intended it that way.