Song of Eternal Sorrow was written by Bai Juyi with his good friend Chen Hong, visiting Xianyou Temple and feeling the story of Emperor Xuanzong of Tang Dynasty and Yang Guifei. Bai Juyi once said in the self-evaluation of "Song of Eternal Sorrow": "Song of Eternal Sorrow has amorous feelings." From this perspective, The Song of Eternal Sorrow is the Song of Eternal Sorrow, which is the theme of the poem, the focus of the story and a touching seed buried in the poem. Although there is a description of Yang Guifei's beauty and Li Longji's debauchery, this is only the need of the structure of this narrative poem, not the theme and emotion that the poet wants to express. The love tragedy between Li Longji and Yang Guifei is the poet's lament, the "long hatred" and the soul of this poem.
The whole poem, especially the ending:
On the seventh day of July, in the Palace of Eternal Life, we secretly told each other in the quiet midnight world.
We hope to fly in heaven, two birds become one and grow on the earth, two branches of a tree. ..
The earth endures, and the sky endures; One day both will end, and this endless sadness will last forever.
Every sentence is tender as water, expressing the poet's full sympathy for this love tragedy that has been spurned by the whole world. The poet did not focus on Li Longji's "Emperor of China, eager to shake the beauty of an empire" or Yang Yuhuan's "If she just turns her head and smiles, there will be a hundred kinds of spells", but infinitely magnified this love tragedy, making the unswerving love the master of poetry, refining feelings from politics, and breaking through the political satire of ordinary literati on this theme at that time, which is exactly where this everlasting regret song touched readers.
Personal opinion, for reference only.