Most of us expect a mirror to reassure us. We imagine endless reflections stretching away, and a firm sense of who we are. The speaker says what you actually find is different: warped, bowed patterns that block the view of past and future alike. The glass shows no person, no time, and no certainty.
Even so, the speaker admits we keep looking. Checking every reflection for some trace of ourselves is called a "bad habit," as if we hoped to be carried back to innocence. But the poem is gentle about it, calling the habit "forgivable."
The closing image is strange and quiet: walls and windows seem to run the film backward and blink in step with us. The mood is wistful and unsettled, a little eerie, but not bitter. The poem suggests that looking for ourselves in surfaces is a very human longing, even when the answer never comes.