The title says it all: this is a poem about burnout, the feeling of being used up. The speaker walks through ruins until they lose themselves, which suggests wandering without direction among things that have already fallen apart. It could be a real landscape or a picture of an inner state, and the poem doesn't insist on one. Then comes a plain admission: "I have become weak and tired." There's no decoration there, just exhaustion stated flatly.
The last image is the strangest and the most striking. A candle is meant to give light, yet here too much light makes it "go bad like a pope." The comparison is odd, and it's hard to say exactly what it means. Judging by the imagery, it may hint at something that burns brightly in service of others, or under heavy expectation, and is spoiled by it. The mood is bleak, spare and quietly wry, with the sudden twist of the final line adding an uneasy edge to the tiredness.