"Richard Cory" is a great example of how a poet can use more than one tone in a poem to achieve a theme that is unexpected or startling.
The speaker's tone in describing Richard Cory in lines one through fourteen is admiring, even envious. He is a man who seems to have it all: the attention of people in town, a kingly physique ("imperially slim"), and a manner that is neither self-aggrandizing nor arrogant. He is wealthy, well-mannered, and the envy of those who encounter him. His gifts stand in contrast to those less well-off who "went without the meat" and waited for things to improve.
The final lines, fifteen and sixteen, are delivered in a dispassionate, matter-of-fact tone:
"And Richard Cory, one calm summer night,
Went home and put a bullet through his head."
Edward Arlington Robinson shifts the tone in his poem at the end to remind readers that we can never fully understand other people's interior lives. The poem was written when many in the country were struggling through the aftermath of a severe economic downturn, and though Richard Cory apparently put a brave face on his situation, he carried repressed burdens.