The shift and the couplet help to explain that even though you don't have money or fame, love is all you need to be happy.
Shakespeare's sonnet follows the traditional structure of a Shakespearean sonnet, which consists of three quatrains followed by a final rhyming couplet. The quatrains develop a particular theme or idea, and the couplet provides a resolution or conclusion to the poem.
In this sonnet, the first three quatrains describe the speaker's feelings of despair and envy, while the fourth quatrain introduces a shift in the poem's tone and content. The final couplet provides a resolution that suggests that the speaker's thoughts of the person he loves bring him happiness that he would not trade for even the most desirable worldly riches.
The sonnet's structure thus plays a crucial role in conveying the poem's meaning, as it allows Shakespeare to develop a series of interconnected ideas and emotions that culminate in a final resolution that reinforces the poem's central message.
~~~Harsha~~~