A man puts on his best suit for a funeral, and the one being buried is an ordinary blue flower. The mix of ceremony and smallness is the poem's quiet joke, but it isn't only a joke. The speaker seems to be taking seriously something the world would barely notice, and the suit suggests real respect, even tenderness, for it.
The next lines widen the view. We "do not live in the light," and we "come to forget everything." The title echoes this: the flower is one more thing slipping out of memory, and so, perhaps, are we. The final image is odd and a little haunting. A coachman, someone who carries people from place to place, "cannot know us / where we were." Judging by the wording, the past can't be reached, even by a stranger whose job is travel. The mood is hushed, gently sad, and strangely dignified, like mourning something so small that nobody else will.