To whom is the lady being compared to in the first stanza in "She Walks in Beauty"?
Byron uses natural elements as a means to both articulate and compare the subject's beauty. Consistent with Romanticism, Byron uses nature as the representation of perfection. This makes its comparison to the woman's beauty an aspect of perfection, something that cannot be replicated. The "night" and "cloudless climes" and "starry skies" of lines one and two are merged with the subject, herself, in line four, when the speaker argues that the subject of the poem is the representation of such beauty: "Meet in her aspect and in her eyes."
Another form of comparison that is present in the first stanza can also be seen in line three. Romantic thinkers were zealous advocates of being able to merge social and political elements of the good with a state of beauty. Beauty was seen as the physical representation of justice and honor, qualities that are intangible and impossible to physically define. Romantic thinkers argued that the aesthetic experience of beauty also represents these realities. Recall Keats' assertion of "beaty is truth" in his work, and one sees how this is a Romantic idea. Byron also does not miss a chance for this in line three where the speaker argues that "And all that’s best of dark and bright" is present in the subject of the poem. In this comparison, Byron is making the argument that the subject is a physical representation of the intangible, apotheosizing her beauty as the physical manifestation of those noble virtues that cannot be quantified.