Shakespeare’s knowledge of the sonnet form allows him to display his messages much better than those who don’t, in this case not all beauty can be observed or touched.
The sonnet is about his mistress yet and her features. Whilst he writes about her he also lists that there are much better things than her, eg “I love to hear her speak, yet well I know That music hath a more pleasing sound.” This does not directly insult the woman yet it says that there are things that are better and he then wraps that up in the end by saying basically that none of these physical imperfections matters. None of her physical forms relate to her soul and mind for that is what Shakespeare describes as “…belied with false compare” which basically means that she cannot be represented for her appearance but for her character. If he had not laid out all of her imperfections then he wouldn’t have given nearly as clear an image.