In this sonnet Shakespeare is parodying the conventional comparisons of traditional love poetry (and specifically, of Petrarchan sonnets). The speaker says that of course his "mistress' eyes are nothing like the sun," nor her lips as red as coral. A traditional love poem might use such clichéd similes to describe the beauty of a woman, but the speaker in this poem, for the first twelve lines at least, seems to refuse to do so.

The poem is structured as a series of comparisons, each one formed as a simile, and most of the comparisons throughout the poem are physical. The speaker thus describes his mistress' eyes, lips, breasts, and cheeks. Bearing in mind that the poem is intended as a parody, the preponderance of physical comparisons is perhaps intended to highlight how superficial those comparisons are. Real love, after all, should transcend the physical.

The first twelve lines of the poem are full of comparisons which seem to suggest that the speaker is not very fond of his mistress, because she doesn't seem to live up to these idealized characteristics of beauty, such as rosy cheeks and snow-white breasts. In the final two lines, or couplet of the poem, however, the speaker turns the poem on its head. He says in these lines that his love for his mistress is more unique, or "rare," than a love which might be lazily described with all of these clichéd comparisons. It is more unique and yet also just as true ("by heaven") as any love that one might have for such a woman who really does have eyes like the sun, and lips as red as coral, and breasts as white as snow.

Similes and metaphors are two of the most powerful weapons in the arsenal of any poet, and Shakespeare certainly uses them quite effectively in sonnet 130 (which begins “My mistress’s eyes are nothing like the sun”). Similes make comparisons by using the words “like” or “as”; metaphors almost identify or equate the two things compared and thus omit such words as “like” or “as”

In the first line of Shakespeare’s sonnet, the speaker wittily disavows the tired, standard, conventional simile comparing a woman’s eyes to the sun. Indeed, throughout this poem, the speaker refutes or denies the kinds of trite comparisons that poets had often made between their beloveds and various material objects. The speaker thereby asserts his own originality as well as his impatience with shop-worn poetic clichés. If a woman deserves to be praised physically, she also deserves to be described honestly, or at least that is one of the implications to be drawn from the phrasing of this poem. Thus, in line 4, the speaker mocks the standard metaphor equating the blond hairs on a woman’s head with golden wires; instead, he confesses that “If hairs be wires, black wires grown on her [that is, his mistress’s] head.” Ironically, the poet contributes to the beauty or effectiveness of his own poem by denying his mistress the kind of stale, predictable praise she might have received from other poets.

Again and again, the speaker mocks the kinds of comparisons used by previous poets to praise their lovers. The first twelve lines of the sonnet amount to a point-by-point rejection of many of the standard metaphors and similes of English and European love poetry: His mistress’s cheeks are not like roses; her breath is not like perfume; her speech is not like music; and her movement is not like the flowing movement of a goddess:

I grant [that is, admit] I never saw a goddess go [that is, walk];

My mistress, when she walks, treads of the ground.  (11-12)

Finally, in the concluding couplet of the poem, the speaker announces that he nevertheless considers his mistress

. . . as rare

As any she [that is, any woman] belied [that is, misrepresented] with false compare. (13-14)

The final two words of the sonnet – “false compare” – make explicit the speaker’s concern with illegitimate similes and bogus metaphors. The sonnet is as much about the writing of true, honest, trustworthy poetry as it is about the particular physical appearance of any particular woman. The poem amounts to a kind of manifesto, implicitly urging poets to tell the truth when they write and admonishing them to be willing to take genuine responsibility for the similes and metaphors they employ.