Summarize the content and theme of Qu Yuan's mourning.

Nine Chapters of Mourning for the Past is the work of Qu Yuan, a great poet of Chu in the Warring States Period. The so-called "mourning" means mourning the fact that the capital of Chu was captured by Qin, humiliated by Qin and the people were displaced. This poem uses flashback method, starting from the fact that Qin Jun was exiled when he attacked Chu nine years ago and traveled eastward with the exiles, and then describes the artistic conception of the poem later. The whole poem can be divided into five layers, each with three sections (four sentences and one section). The first three layers are memories, and their lyricism is mainly expressed through narration; The fourth layer expresses the mood at that time, and the fifth layer thinks about the causes of national and personal tragedies. Random words summarize the whole poem from two aspects: emotion and structure. Although the poet misses Ying Du day and night, he can't go back to Korea to serve his motherland because of exile. The whole poem is carefully organized and integrated.