The speaker is walking a hard, uncertain path and can't leave it. The ground is broken cobble, the air is thick with mist and grit, and the walls on either side hem them in. The poem reads like a journey, but it is also easy to take it as a picture of a life moving in one direction whether we like it or not.
The speaker's feelings are mixed. They move hesitantly, "not light of foot," yet they never settle into comfort, since there is "no complacency." The walls show no weakness, so there is no hope of escape, and the speaker calls them a "confining fate." Being "driven only forward" suggests a force pushing from behind rather than free choice.
The mood is heavy, tense and resigned. The short, abrupt final line, "End," lands like a door shutting, and the word "suddenly" makes it feel both unavoidable and unexpected.