Shakespeare's "Sonnet 29" is about the despair the speaker feels when he has faced some disgrace of fortune--perhaps he can't pay a bill or a play was badly acted or poorly received--and as a result feels like an outcast from society because of the disgracing glances from other men's eyes. It is times likes this that he cries in vain to heaven and abhors his successes and failures alike.
He wishes he were "rich in hope" like someone else who has loving friends or that he had the talent of this other one or the intellect of that one, and he is most unhappy with his own life and talents. Then he thinks of the his beloved and becomes like a lark at daybreak singing at "heaven's gate" and, when thus thinking of the beloved, would not trade places with kings: "I scorn to change my state with kings."
The conclusion of this slide into melancholia and depression of "Sonnet 29" is that the speaker's gloom and despair are turned to joy and happiness at the mere thought of the beloved who is so good at heart that "thy sweet love" can lift the speaker to soar above kings.
Basically this speaker mentions all the things that are going horribly wrong in his life (or at least he sees it that way). Then at the end, when he's been horribly down on himself, his mind wanders to the woman he loves. Thinking about her for just a minute makes all that other bad stuff go away for him, and he decides that since he has her, he wouldn't want to be anybody else!