How does Shakespeae glorify his friends in sonnet 18?

Shakespeare takes an image that is normally used to compliment an individual and twists it. He's saying that he can't even compare his subject to something as beautiful as a summer's day because their beauty exceeds it. The subject is "more lovely" than a summer's day. He then points out the flaws of the summer, such as it's transience (we all know fall seems to come way too soon) and sometimes the sun (or "eye of heaven") is too hot or hidden from view. He then says that while every fair, or beautiful, thing eventually becomes less beautiful that's not the case with the person he is writing the Sonnet for. Thier "summer" is eternal and not even death can take it away because their beauty is immortalised in his poem. Sometime too hot the eye of heaven shines, And often is his gold complexion dimm'd; And every fair from fair sometime declines, By chance or nature's changing course untrimm'd; But thy eternal summer shall not fade Nor lose possession of that fair thou owest; Nor shall Death brag thou wander'st in his shade, When in eternal lines to time thou growest: So long as men can breathe or eyes can see, So long lives this and this gives life to thee.