Two short lines set up a sharp contrast. The speaker is far from home on what they call a "cold business," which suggests work that is impersonal, maybe joyless, and carried out among strangers. Yet they carry something private: a "secret fire," which the poem then names as "a piece of gold." Fire and gold both suggest warmth and value, so this could be a memory, a love, a belief, or a creative spark that the speaker keeps hidden and protected. The poem never says which, and that vagueness lets us fill it in ourselves.
Then comes the final line: "Infinite, tedious rain." After the glow of the first line, it lands like a bucket of water. The rain seems endless and dull, pressing in on the speaker's surroundings. The mood is one of quiet endurance. The speaker isn't dramatic or despairing, just weary, and holding on to one small bright thing while the grey world drips around them.