Classic and Romantic, According to Santayana

The Last Bookstore of Los Angeles turned up a copy of The Last Puritan, where I found a vaguely remembered passage in Part V, Chapter IV. In the novel, the passage forms part of a letter from the cosmopolitan Marius (or Mario or Vannie) Van der Weyer, now an officer of the FC convalescing at Oxford, to Oliver Alden, the puritan of the title, now an officer of the AEF serving in France:

You remember those two poplars at the entrance to the little tea garden? They were particularly solemn and graceful that afternoon, swaying in the breeze, now intertwining and now separating their branches, as if two green spires all composed of pinnacles, like Saint Mary's, had begun to dance, locking arms and touching cheeks in time to the windy music. "If my Latin weren't so rusty," I said to Cooly, "and my Greek so inadequate, I should compose an epigram about those two poplars. Quite classic, that straightness of theirs, that amplitude, that murmur, and that sadness."

Cooly tossed his dyed plumes, as a bird does when drinking, and slowed for a moment, above his loose low collar, a prodigious Adam's apple moving up and down. The man actually seemed inspired, only, as a lyric Apollo he is rather a barebones, and looks too much like Abraham Lincoln. After a moment he began chanting:

    "Ambigua Zephyro Geminae dum fronde susurrant

       cedit ab immemori muta sorore soror."

"Hear, hear", I cried, "but please say it again. In Latin you have a slight English brogue. I'm not sure I've caught it all."

"Impossible, impossible. Not good enough. Not worth remembering. But I'll say it in English."

Again Apollo shook his ambrosial locks, again Adam's apple moved up and down, and the words flowed irresistibly: 

"Poplars, twin sisters, whispering side by side:
The winds unite them, and the winds divide."

"Really, mes compliments. But the modern version is not quite faithful. There is more and less in it than in the original."

"Inevitable," he rejoined, still liturgically and under the spell of the Muse. "Poetry can never say the same thing twice."

"Granted. But will you explain this. Why is your English epigram classical and your Latin epigram romantic?"

"Because," he replied without the least hesitation, "when we move upward from chaos, we aspire towards truth, perfection, and simplicity: but when we reflect and turn inwards from the highest achievement, we find sorrow and disillusion and a murmur of the winds."

The passage has stayed in my memory for a good thirty years or more (though I must have had the classic/romantic pairing switched), but I would hesitate to say that I wholly understand it.