Journeys can be fun. (And we don't mean these guys, though we can get down to "Don't Stop Believin'" any time.) They can be full of adventure. We get to see new, beautiful places when we travel. But, in "A Poem of Changgan," journeys are a source of pain and heartbreak. That's because the journey in this poem separates the speaker from her husband. Even though the husband's journey is the catalyst for the speaker's sadness, it also reveals how much this speaker loves her sweetheart. The depth of her feelings for her husband, in other words, is revealed because of the journey that separates her from him.
Line 15: The speaker's hubby goes away on a long journey. This journey is the source of all the speaker's misery, because it separates her from him. The journey, in other words, is at the center of the conflict and sadness that the speaker experiences in this poem.
Line 16: The speaker tells us that her husband's journey takes him "[t]hrough the Gorges of Ch'u-t'ang, of rock and whirling water." This description is important because it suggests that the husband's journey is dangerous. What if he falls down one of those gorges or drowns in that whirling water? This description raises the question of whether the husband will return safely. Will he come back from this dangerous journey?
Line 27: By referring to her hubby's return here, the speaker suggests that she's still full of hope, despite her husband's long absence. But is she deluded? After all, her hubby's had to go through some seriously dangerous terrain, and it's a question whether he will ever come back, especially since it's been so long since he left.