Stanza 1: The author describes the beauty of a walking woman by comparing her to a clear, star-filled night sky with the use of a simile. Her beauty, particularly her eyes, is the result of a perfect union of light and dark. The delicate balance of light and dark is comparable to heavenly light.
Stanza 2: Just a little more shade or a little less light would disturb the perfect balance and lessen the woman's beauty. Her beauty is so striking, it is evidenced in every strand of her raven-colored (black) hair, which hangs gently upon her face. Her expressions are angelic and reflect her emotions and purity.
Stanza 3: On the woman's cheeks and above her eyebrows (her forehead), her winning smile and glowing tone appear, softly and calmly, but still subtly noticeable. She spends her days doing good deeds, and her features reflect her goodness. She is virtuous and has a peaceful mind and an innocent heart.
One of the themes of Lord Byron's "She Walks in Beauty" is the harmonious balance between light and dark to achieve perfection. Byron describes the woman's beauty as a delicate and exact marriage between light and dark, just as a starry sky contrasts and combines light and dark (the bright, illuminated stars against the clear, dark sky). He says if this balance were altered even in the slightest way, the woman would not be as beautiful. Byron is suggesting that for perfection to exist, there must be a precise, harmonious union between the contrasting forces of light and dark.