In the revision process, you improve your reading skills and your analytical skills. You learn to challenge your own ideas, thus deepening and strengthening your argument. You learn to find the weaknesses in your writing. You want someone else to read your writing before you revise it so they can give you some notes and ideas on what to add, remove, fix, etc.
Since most readers did not share your exact experience, they can help you figure out what details might be missing from your poem. They can also tell you what it's like to read your poem, giving you some ideas about what you might want to change to improve your poem's impact. A reader can tell you where the poem's message is strongest and where it is weakest.
