"Finished" is a tiny poem about walking away from a job and what comes after. The speaker ends a contract, and the first gesture is odd and a little playful: tipping a hat to the office, like a polite farewell to an old acquaintance rather than a angry exit. There's no bitterness here, just a calm, formal goodbye.
The last line carries the real feeling. Once work is over, the speaker makes "an abstract home of the night." That's a strange, interesting phrase. Night becomes a place to live in, but an abstract one, without walls or fixed shape. It suggests freedom, but also a bit of uncertainty, since the speaker has left behind a structure and has nothing solid to replace it yet.
The mood is quiet, relieved and slightly wistful. It feels like the moment after a long day ends, when you're free but not sure what that freedom looks like.