Sara Teasdale's four lines imagine two people who have crossed paths again and again without realizing it. The speaker looks back and wonders how many times they must have met on an ordinary street, passing each other the way strangers do. Nothing marked those moments as special, so neither person stopped or looked twice.
The most striking image comes at the end. They "passed / The door of heaven and never knew." Heaven here seems to stand for the love or happiness they might have shared, and it was right there, close enough to touch, yet they walked by. Calling themselves "children of chance" suggests that their lives were ruled by luck rather than design, and that luck failed them.
The mood is quiet and wistful, with a small ache of regret. The speaker doesn't sound angry. She seems struck by how easily something precious can slip past unnoticed, and how much of life depends on moments we don't even recognize as they happen.