"and the portrait show seems to have no faces in it at all, just paint/ you suddenly wonder why in the world anyone ever did them"
This line, which occurs in the middle of the poem, emphasizes the speaker's surprise at his realization that his lover's form is preferable to any portrait he has seen. This is significant because of the central role visual art plays in the speaker's life; previously, perhaps, his love for paintings rivaled his feelings for his beloved. But now real life has suddenly become more beautiful than even the most famous of paintings. When compared to this lover, these great works seem to lose their power and their meaning.
"and what good does all the research of the Impressionists do them/ when they never got the right person to stand near them when the sun sank"
This line explicitly articulates a sentiment the speaker maintains throughout the poem: when considered in the context of the speaker's lover, artistic masterpieces suddenly become less remarkable, more commonplace. It doesn't matter how great the Impressionist masterpieces may be—they are missing an essential feature: namely, the perfect sitter, which is the speaker's lover.
"it seems they were all cheated of some marvellous experience/ which is is not going to go wasted on me which is why I'm telling you about it"
In the last lines, the speaker explains his reasons for writing the poem. Artists like Impressionist and Renaissance masters missed out on painting the perfect model—the speaker's lover—and the speaker refuses to let this moment go unrecorded. The speaker creates his own masterpiece with language, which can be shared and remembered the same way that famous works of art are visited in museums. The "you" in this line is ambiguous, and could refer to the lover, the reader, or both.
