The speaker of "Epilogue to Lessing’s Laocoön" walks with his friend through Hyde Park, discussing German writer and dramatist Gotthold Ephraim Lessing's famous essay Laocoon.
As the essay expresses the limitations of painting and poetry, the friend questions why painting and music have always been more successful than poetry. He provides examples to prove his claim, insisting that even the Greeks - who valued all arts - found painting and music most powerful.
As the speaker listens to his friend, they leave the path and step onto the grass. The speaker then takes a moment to describe the scenery, and in the process has a burst of insight — this is the limitation of a painter's art. A painter can only capture a single, fleeting moment of life, rather than a period of time. Thus, he must choose his moment wisely.
He pauses again to listen to the sounds of the world around him, and then realizes that the musician faces a similar limitation. Though he can capture more than a single moment in his work, he only has a select number of notes with which to express it. Thus, he must like the painter choose wisely, selecting the proper notes to capture his meaning.
The speaker and his friend reach a section of the park full of people in constant motion, and at last the speaker realizes the power of poetry. A poet must be a painter and a musician all at once, for he must capture the movement of the world, which is an extremely difficult task. He must tell of life's pleasure and pain, its rest and strife, and display how it changes from year to year. In short, he must describe the lives of people. Everyone and everything is affected by the movement of the world, and a poet is responsible for capturing that. Therefore, poets face the greatest labor of any artist, and deserve more reward.
In order to understand this poem, it helps to know more about Lessing's Laocoön itself. Laocoön, as previously stated, is an essay on the limitations of painting and poetry. In it, Lessing argues that it is foolish to write poetry using the same devices one would use to paint. Painting and poetry each has its own character, and should not be approached from the same direction.
In his "Epilogue" to this famous essay, Arnold adds that not only are the mediums very different, but that poetry is in fact much more laborious, since it requires capturing the entire movement of the universe, while painting does not.
Whereas some of his poems are looser and more free-form than this one, Arnold deliberately uses a strict structure here to emphasize how difficult it truly is to write good poetry. That being said, the poem is not overly complex - it employs an AABB rhyme scheme and and iambic tetrameter meter, both fairly simple as poetry goes. The lines are short and they move fast, which highlights the poem's conversational tone. And yet he communicates very complicated ideas alongside a simple narrative without deviating from this strict form, reminding us through the telling that poetry demands rigor and yet can capture an entire thought process.
Behind the poem's argument is a love of language. It is telling that Arnold's final examples of great poets are Shakespeare and Homer, best known less as 'poets' than as storytellers. While he could be thinking of them in terms of rhyme schemes and the like, it is also plausible that Arnold means poetry to include more broadly any use of language as art. This certainly supports his implicit argument that the best art does not have to be so selective - there is an infinity of words one can use, which is not true about notes on the musical scale. No matter how one feels about Arnold's argument, it is clear that this poem unambiguously revels in the potential that storytellers have to affect us and capture the nuances of life.
Arnold alludes to many famous poets, musicians, and artists in this poem, which provides some real world examples to prove his point. It is one thing to claim that poetry is more difficult than other forms of art, and another thing to call upon recognizable names in the art world in order to prove it. One of the very last lines reads "Beethoven, Raphael, cannot reach/ the charm which Homer, Shakespeare teach." Beethoven and Raphael are composers and painters, respectively, and Homer and Shakespeare are poets. Ultimately, as all four of those names are canonical by this day and age, the poem's argument remains fascinating, if not necessarily compelling for someone who does not already agree.