Answer: to express long, complex ideas and emotions
Explanation: In "My Last Duchess" by Robert Browning, the poet uses run-on lines to express long, complex ideas and emotions. Enjambment is a literary device that occurs when a verse does not end at the end of the line but runs on to the following line. There is no punctuation mark at the end of the line. This poem is a single long stanza. This suggests fluency and the capacity of expressing long and complex ideas and emotions.