“Where the Sidewalk Ends,” by Shel Silverstein, is at once a melancholic and hopeful poem. Silverstein creates a contrast between, on the one hand, a melancholic place, characterized by “dark street[s]," “asphalt flowers," and smoke that "blows black," and on the other hand, a place “where the sidewalk ends,” where “the grass grows soft and white" and “the sun burns crimson bright.” These two places are symbolic of adulthood and childhood, respectively, as indicated by the fact that the children are the only ones who “know / The place where the sidewalk ends.”
The place that symbolizes adulthood seems to be full of darkness, whether it be in the form of the black smoke, the “dark street[s],” or “the pits where the asphalt flowers grow.” This darkness connotes ignorance, emptiness, and, perhaps, immorality. The darkness of this place is also emphasized in contrast to the brightness of the other place, where the grass is white and the sun “burns...bright.” In contrast to the darkness, the brightness here connotes clarity, innocence, and purity.
In summary, the speaker seems to be suggesting that childhood is a time of clarity, innocence, and purity, whereas adulthood is a time characterized by the loss or absence of those virtues. We have clarity in childhood because life seems so simple; in adulthood, life seems to become infinitely more complicated. In childhood, we are innocent and pure; in adulthood, we have succumbed to the temptations of sin.
The speaker in the poem represents childhood and adulthood metaphorically as real places, because in this way he can be hopeful of returning to the simplicity and innocence of his childhood, leaving the complications and sinfulness of his adulthood behind. The meaning of the poem is that we should all endeavor to make this same journey—from a life of sin to one of innocence, and from a life of complications to one of clarity.