How to understand the difficult things, the night snow in the building and the autumn wind of the iron horse in the land tour of Book Wrath? What does the last couplet express the author's thoughts?

"Things are hard": Things are hard. I didn't expect the road to killing the enemy and serving the country to be so difficult? I thought that if I dedicated myself selflessly and served my country wholeheartedly, my country would be fulfilled by me. I didn't expect traitors to obstruct and destroy me and be deposed many times. Express the anger and sigh accumulated by the poet. "It snows at night in the building, and the iron horse is in the autumn wind": It describes Song Bing's resistance to the invasion of Jin Bing in the southeast and northwest, and it is also a summary of the poet's past travels. In the thirty-first year of Shaoxing, Song Gaozong (1 16 1), Yan Hongliang, the gold owner, invaded the south, and Song Jun refused to defend it in Guazhou, and then the army of nomads retreated. This is what the last sentence refers to. In the eighth year of Ludao (1 172), Luyou attended the Wang shogunate in Nanzheng. The poet and Wang Yan actively planned to invade Chang 'an, once crossed the Wei River and passed the three passes with the Nomads Normal University. The next sentence refers to this. The glorious past summarized in these two sentences is in sharp contrast with the present situation of "intentional killing of thieves and inability to return to heaven". "I am afraid to wait for me and hate him for another year." Why does the poet cry when he wants to return to the Central Plains? From the perspective of poetic art, these two poems also show Lu You's great poetic talent. When the "building ship" (a magnificent warship) is combined with the images of "night snow", "iron horse" and "autumn wind", it is two open and magnificent battlefield scrolls. Image selection is very clean and typical. Pave the way for the later article "Stuck on the Great Wall". Tail couplet: Tail couplet is also written with allusions. Zhuge insisted on the Northern Expedition. Although he is a "true teacher", he is famous all over the world. "No one is as good as Millennium". After thousands of years, who can compare with it? Obviously, the poet's code deliberately belittles the mediocre villain in charge of the ruling and opposition parties, indicating that his ambition to restore the Central Plains will also be "famous in the world". The poet can't find comfort in reality, so he has to put his soul longing for comfort in the future, which is naturally helpless. The poet has to pour out his frustration when he is depressed. Through Zhuge Liang's allusions, I pursue the achievements of the sages, indicating that my patriotic enthusiasm will never change, and I am eager to emulate Zhuge Liang and display my ambitions. Looking back at the whole poem, we can see that every sentence is full of gas, and every word is full of gas. Poetry is full of anger.