The speaker in “Sonnet 29” leads a life full of trouble and great unhappiness. As he tells us in the very first line of the poem, he finds himself in “disgrace with fortune and men's eyes.” It is clear from this sad lament that many people, for one reason or another, do not respect the speaker as they should.
As a consequence, the speaker looks about him and becomes jealous of other men and their good fortune, “Desiring this man's art and that man's scope.” On the whole, he gives the distinct impression that he's not very happy in his own skin and would much rather be someone else. This is a perfectly understandable attitude to have if, like the speaker, you find yourself in an “outcast state.”
But just when these unhappy thoughts bring the speaker to the point of self-loathing, thoughts of his beloved enter into his troubled mind and provide him with much-needed solace. His beloved's sweet love gives the speaker so much that he no longer wishes to change places with anyone, not even a king. In other words, he's happy with being himself; he doesn't want to be anyone else. Such is the remarkable, transformative power of love.