What is Cui Shu's poem expressing his knowledge in The Yellow Crane Tower?

Dear landlord, this is "but I look home, the dusk is getting dark, and the mist of sadness is filled on the river waves." Generally speaking, whether it is a poem or an article, the theme center and the author's thoughts are always at the beginning or end of a sentence.

Judging from the whole poem, this poem is at the end of the poem. In addition, no matter from the artistic conception of the poem or the implication of the author, these two sentences undoubtedly express the author's thoughts and feelings. This sentence is also mentioned in Chinese textbooks.

Thank you.