From the author's own point of view, there is a contrast between the heroic age and the present decline, and between the heroic heart of serving the country and his old age. Judging from the situation at that time, Lu You's yearning for Zhuge Liang's achievements in the Northern Expedition was also a hidden contrast with the fact that most court officials and ministers were not enterprising. The use of contrast makes the emotional orientation of poetry particularly prominent and enhances the artistic appeal.
See textbook P96 for the answer analysis.
Knowledge points of this question: Lu You,