Clear. What is the theme of Gong Dingzi's Thinking Over Jinling?

This poem expresses the poet's feelings on the last day when he returned to Jinling from northern Guangdong. Write the first two sentences about Jinling historic site. On the day of enjoying spring in March, leaning against the railing, bathing in the east wind and looking at the bright spring scenery, how cheerful it should have been! However, the poet vaguely heard the lingering sound of the flower melody in the back garden of Yushu. "Thousands of families have become weeds because of a flower in the backyard." (Liu Yuxi's Taicheng) So I can't help but think of the story that Chen Houzhu died after indulging in debauchery. The poet gazes at the vast Yangtze River, but he can't help but think of the historical fact that Emperor Wu of Jin ordered Wang Jun to attack Wu, "Chihiro iron lock sank to the bottom of the river, and a stone fell out" (Liu Yuxi's Random Thoughts on the Old Times of Xipao Taishan). Nowadays, the iron lock that blocked the river in those days has dissipated like wild smoke in the countryside. These two poems are tit-for-tat, and the scenery description and allusions are perfectly matched. The first sentence implies that the axe king and Zhu Yousong of Nanming were dissolute, and the second sentence shows that the Qing soldiers crossed the river and the axe king was captured, which made the ending of Nanming more obvious. At the same time, the poet's yearning for the motherland and his sad feelings are integrated. The third sentence is not about the past of Jinling, but it is also internally related to the first two sentences. On the fourth day of the ninth year of Yonghe in the Eastern Jin Dynasty (353), Wang Xizhi wrote the famous Preface to Lanting at a party with friends. At this moment, the poet thinks of the sigh in the preface, "I am delighted with it, and between pitching, it has become a thing of the past, so I still have to be delighted with it", which adds a sense of ups and downs. On the basis of this poem, the last sentence returns to the old story of Jinling and pushes the whole poem to a climax. "Jiangshan is still the same, and personnel are completely different." The evergreen green hills in Jinling sent away the Six Dynasties after Sun Wu, didn't they also send away the Zhu Ming Dynasty, which once built Jinling as its capital? The past and present are memories, but they are gone forever after all. Through this poem, the poet, who was forced to bend over to be incorruptible, expressed his helpless regret and nostalgia for his old country, and also showed his elegant and graceful demeanor.