This is perhaps Byron's most famous poem as it caputres the sight of a beautiful woman that the speaker has seen at a ball. She somehow manages to paradoxically combine the best aspects of both light and dark, and in her character the poet can sense purity, calm, innocence and sweetness. I don't necessarily think that Byron had a purpose other than to commemorate what was to him a beautiful and impactful moment that he desires to set down for all time in this poem. Byron presents us with an amazingly detailed and beautiful picture of beauty itself, as characterised by this woman, and in particular the last stanza is notable for what Byron is trying to convey:
And on that cheek, and o'er that brow,
So soft, so calm, yet eloquent,
The smiles that win, the tints that glow,
But tell of days in goodness spent,
A mind at peace with all below,
A heart whose love is innocent!
What is remarkable about this woman is the way that her external beauty, "The smiles that win, the tints that glow," actually reflect the woman's internal beauty and her kind and virtuous soul. This woman, unlike others, the implication is, has a beauty that reflects her own internal beauty. Beauty is not necessarily just skin deep, after all.