The speaker is on a train, and the journey feels like a image of life itself: he is moving, but he has no say in where he is going. He admits to having "no control over destiny or destination," and the plain, flat wording makes that helplessness sound like a quiet confession rather than a complaint.
The other passengers make the feeling stronger. Their faces show brief "flickers or flashes" of expression, but the speaker can't take pride in them, as if he can't claim any real connection with these people. They come and go "with the same indifference," neither noticing him nor leaving a mark. The poem ends on the view outside the window, where shadows of distant houses, hills and trees just keep passing. Nothing stops, and nothing is held onto.
The mood is detached and a little lonely. It's calm on the surface, but underneath there is a sense of drifting, of watching life go by without steering it.