What kind of thoughts and feelings did the poet express in To the Frontier?

In the spring of the 25th year of Kaiyuan (737), Wang Wei went to the northwest frontier fortress to visit Cui, the assistant envoy of Hexi who defeated Tubo. This was actually excluded from the court. This poem is about this task.

The poet wrote down the experience of this mission with concise pen and ink. "I want to ask over there by bike", which says I'm going to the border to express my condolences to the soldiers. How far should I go? "Returning to China" means going to Juyan, which is far away in the northwest frontier. The mountain is high and the road is far. The poet felt that he drifted like a "Cai Peng" and entered the lake field like a "wild goose". He not only talks about things, but also writes about scenery, and even conveys his unspeakable inner feelings in narrative writing. After a long journey, the poet finally "rode to Xiaoguan", but he didn't meet the general. The story seems to continue, but the poem comes to an abrupt end, leaving room for aftertaste.