I may agree or disagree with Mr. Scruton for reasons different from his but here he sets up an example which I find interesting.
Brooks is pointing to several distinct features of poetry. First, there is the fact that a line of poetry can express several thoughts simultaneously, whereas a paraphrase will at best lay them out in succession. For instance, the line 'bare ruin'd choirs, where late the sweet birds sang', describes both the trees in autumn and the recently ruined choirs of the monasteries that were still frequented in Shakespeare's youth. A paraphrase would give one of those readings, and then the other; but the power of the line consists partly in the fact that you hear them together, like simultaneous voices in music—and then the doom of autumn invades the image of the ruined monastery, just as the idea of sacrilege invades the image of the leafless tree.
Secondly, there is the fact that poetry is 'polysemous', developing its meaning on several levels—the levels of image, of statement, of metaphor, of allegory and so on. This point was made seven centuries ago in the celebrated letter to Can Grande della Scala explaining the allegorical meaning of the Divine Comedy—a. letter normally attributed to Dante—and in Dante's Convivio. And it became a commonplace of late medieval and early Renaissance poetics. A paraphrase would have to spell out the levels of meaning separately; whereas the power of poetry depends on their being presented simultaneously.
Beauty, A Very Short Introduction Roger Scruton 2011 (p. 94)