The tone of this sonnet is down-to-earth and pragmatic, and rather wry. It paints a picture of the poet’s beloved in realistic terms rather than indulging in the kind of hyperbole that love poets, and particularly sonneteers, liked to indulge in, as exemplified in Sir Phillip Sidney’s sonnet series, Astrophil and Stella. In fact the poem very consciously undercuts this kind of inflated approach to love poetry.The speaker remarks emphatically that his ‘mistress’s eyes are not like the sun’ (1), her lips are not 'red' as 'coral' (2), her breasts are not 'white' (3) and so on.
The three quatrains of the sonnet are taken up with this line-by-line demolition of the usual kind of imagery to be found in love poems which make such exaggerated claims for the beauty and allure of the beloved. The crux is to be found in the final couplet:
And yet, by heaven, I think my love as rare
As any she belied with false compare.(13-14)
The poet therefore concludes that although his mistress is no ravishing beauty, his love for her is genuine and she is as valuable, as ‘rare’ as any of these women who are extravagantly praised by other poets. In fact the ironic implication is that these other women are not rare at all, as they are all portrayed in a similar manner.
In the last line the speaker bitingly refers to the usual love similes and metaphors as ‘false compare’. Thus he makes clear his disdain for the kind of unrealistic picture that most love poets tend to paint, while paying tribute to true love which does not depend on false representations.