Why is it significant that the poem "Stopping by Woods on a Snowy Evening" is set in the winter on the darkest evening of the year?

By “the darkest evening of the year,” it is most likely that the speaker refers to the Winter Solstice, the shortest day of the year on which the evening would begin early. When it is snowing heavily, however, the moon and stars will be hidden, so it could be a different night.
Riding in the dark, the speaker will not easily see the path and the woods beyond also are not lighted; in addition to being “dark and deep,” they seem lovely to the speaker. The snow both obscures any light from the sky and provides the only apparent light through its white or downy flakes. The speaker stops briefly to watch the woods “fill up” with this whiteness. Metaphorically, this phrase is often likened to despair or a spiritual “dark night of the soul”; the snow, by extension, would be hope or salvation.