What is the purpose of the figurative language in this excerpt?

Follow the directions (and example) given to create your own sonnet. william shakespeare's sonnet 130 my mistress' eyes are nothing like the sun, coral is far more red, than her lips red, if snow be white, why then her breasts are dun: if hairs be wires, black wires grow on her head: i have seen roses damasked, red and white, but no such roses see i in her cheeks, and in some perfumes is there more delight, than in the breath that from my mistress reeks. i love to hear her speak, yet well i know, that music hath a far more pleasing sound: i grant i never saw a goddess go, my mistress when she walks treads on the ground. and yet by heaven i think my love as rare, as any she belied with false compare. instructions: write fourteen lines of iambic pentameter. use a sonnet rhyme scheme. use the first eight lines to set up your idea (the octave). use the last six lines to conclude your idea (sestet). (variety may be added by including a substitute foot from time to time such as the two anapests in line 3 above.) work in small groups giving each other feedback. reading the sonnet aloud allows you to hear the words and rhythms of the lines. generate questions that will clarify the use of words and forms. for example: was the idea of the sonnet presented in the first eight lines? how was sound used to enhance the meaning of the sonnet?