The surprising last line of the poem is ultimately where the whole poem is headed. As the previous post noted, the pace of the poem is driving us through this description of Cory and of the regular people of the town, and we are getting a very clear description of a very fine man, but his suicide comes as a shock. We immediately ask ourselves, "Why would he, who seems to have everything, kill himself?" That is EXACTLY what the speaker / poet intends for us to do. The speaker is purposely establishing the irony of the last line, and it ends up being his judgement of Richard Cory, even though it is unstated. The speaker recognizes that there must have been a shallowness in Cory, or an appearances vs. reality problem in Cory's life for the man to decide to kill himself. All of the previous lines establish the outward appearance and behavior of Cory, or of the people he passed by, but the speaker and we never know the inner workings of the man himself.
The speaker uses plain, everyday activities of location and eating, and the words of the speaker locate the speaker and fellow admirers of Cory as ordinary people whose lives never rise to any high level of achievement. The speaker suggests Cory's riches and accomplishments. Gentleman is a word suggesting high, noble birth and elegant manners and accomplishments. The word choices of “sole to crown” and “imperially slim” put Cory into an elevated class, whereas the contrasting phrases would be appropriate for ordinary persons. he repetition of And at the beginning of six lines keeps the poem moving rapidly, driving us on from line to line, and suggests that all Richard Cory’s qualities are connected. The repetition of the conjunctions is a rhetorical device called “polysyndeton” (the use of many connecting words). The positive characteristics that the speaker alludes to Cory were his physical appearance, manner of dress, gentle speech, and the ability to speak directly to people while maintaining his power to impress them.