The function of expression: the expression in poetry mainly makes the poet's position and viewpoint more clear and lyrical, such as "making XX more prominent through comparative expression", paying more attention to lyricism and discussion; Rhetoric in poetry is mainly to make the written language vivid and easy to understand.
The last sentence: "I don't want to send wine to Chunchun, it is raining at dusk." Spring is coming home. I'm going to raise a glass to send spring. Spring is quiet, but it is raining at dusk. "Sending wine to spring" is a sign that you want to keep spring but you can't. It's raining at dusk is not so much a raindrop in nature as a sad tear of the author. The whole poem, from cherishing spring to seeing off, always reflects the poet's true feelings of infinite love for youth.