The speaker remembers someone whose smile left them in awe. At first it seems they are praising her looks, but they quickly correct that: it isn't her bright, chalk-white teeth that matter. What strikes them is what the smile seems to stand for, a kind of perfection and innocence that feels almost too pure to be real.
The last lines carry the emotional weight. The speaker admits that life can be dark, and the poem suggests this darkness is heavy and persistent. Yet her smile is enough to push it back. The image of light "devouring" the dark is striking, because devouring is a forceful word for something so gentle. It makes her smile feel powerful, almost protective.
The mood is tender and grateful, with a hint of sadness underneath. The speaker doesn't tell us what the darkness is, but the way they cling to this memory suggests how much the smile mattered to them.