Assuming this is about the sonnet 73 of Shakespeare
Explanation:
The sonnet consists of 14 lines. In the English method of how the sonnets work, the sonnets are divided into four parts if one follows the rhyme scheme and the thematic possibilities of the text while the original Spanish form had 3 divisions.
The first four lines will form the first para,
The 5-8 and 9-12 lines will form the second and 3rd paragraph respectively,
And the last two lines that rhyme to each other will form the sonnet's 4th paragraph as a couplet.
The sonnet is usually found to have a reversal after the 8th line and contains an aphorism in last to, which is evident in this division.