The speaker of this sonnet has been rejected by another person, perhaps a lover. The speaker has lost his beloved to a rival. This sonnet is said to belong to a group of 10 Shakespearean sonnets called the "Rival Poet Group." These deal with the theme of rejection.
The first word of the sonnet is "farewell." He has said goodbye and this signifies that the relationship has ended. The speaker is self-deprecating and indicates that he is simply not good enough for the person who has rejected him. That is to say he is not good enough as a lover and/or as a poet.
However, we can also see how the speaker is mocking his lover because of the legal language he uses. He says the "charter of thy worth gives thee releasing." A charter carries legal and official implications and this suggests that his lover is from a higher social class and standing. The speaker therefore suggests that he has been rejected because he is in a lower social position. So, we can interpret his rejection in these two ways. He feels that he is not good enough and/or he feels that he has unfairly been rejected on the bases of social standing or some other social aspect.
He seems to accept that there are legitimate reasons for being rejected. "So thy great gift, upon misprision growing, / Comes home again on better judgment making." The misprision (error) of being in a relationship with the speaker grows more clear when he considers things with better judgment. Again, the speaker understands why he has been rejected, but there is a sense (mentioned earlier) that it is unfairly based on some social cue. We can read this mocking tone because the speaker uses legal jargon (charter, bond, patent) to describe a loving relationship.